The early voting is done, scores of ballots have been cast by mail, and preparations are underway for primary election night virtual celebrations and concessions, as long as the winners and losers can be fairly determined after the polls close at 8 p.m. Then it's on to the Nov. 3 general election for Tuesday's winners.

Tuesday's elections feature one of the nation's most watched U.S. Senate contests, an opportunity for one Democrat to emerge in the race for an open U.S. House seat, and battles that are likely to leave seven candidates situated to fill Massachusetts House seats on Jan. 6, 2021. Up in Lowell, a House Democrat wants voters to re-elect him while he fights federal fraud charges. A Brockton Democrat is looking to hold on to his Senate seat after being punished by his colleagues in connection with his 2018 drunk driving case. And two years after two top House Democrats lost primary races, more than a dozen candidates will try to topple sitting House and Senate Democrats.

While there's been a lot of hype from the candidates and media and voting opportunities have been expanded this year, voters have often tuned out the primaries. According to data from Secretary of State William Galvin's office, turnout in the last five primary elections held during presidential elections years has averaged 11.2 percent. Galvin plans a pre-primary media availability on Monday morning.

Here are some storylines and people to watch in Tuesday's elections:

U.S. Senate Democratic Primary

There's more at stake in the race between U.S. Sen. Edward Markey and U.S. Rep. Joseph Kennedy III than just one of the state's two Senate seats. The legacy of the country's most well-known political dynasties is also on the line. Kennedy took a risk in taking on an incumbent, and if he comes up short -- as recent polling suggests he might -- he would be the first Kennedy to lose a Massachusetts political race, stunting what has for several years now looked to be a promising national future. The Markey-Kennedy matchup has been circled for quite some time, ever since early polling suggested the four-term Congressman had a healthy advantage entering the race against a long-time fixture of Washington. The COVID-19 pandemic took some of the wind out of the race's sails this spring, but the two men representing different generations in recent weeks have gone toe-to-toe over their records, the Kennedy brand and the behavior of their supporters online. Kennedy has knocked Markey as someone out-of-touch with the people of Massachusetts, but Markey has proven resilient. Few would have predicted in the early days of the contest that it would be Markey, at age 74, who would become the dominant force on social media, and go from a politician who had remarkably little name recognition despite his longevity to a darling of the left and youth movements. The Markeyverse, as his online supporters refer to themselves, have turned him into a virtual environmental superhero, thanks to his co-sponsorship of the Green New Deal, and the incumbent appears to have momentum moving into Tuesday, which is the last day for people to vote in person. But voting has actually been going on for weeks, and with widespread mail-in-voting happening for the first time in Massachusetts, who that might favor is anyone's guess. Meanwhile, on the Republican side of the ballot, Boston lawyer and Dover resident Kevin O'Connor is taking on repeat candidate Shiva Ayyaduai, an MIT-trained engineer. - Matt Murphy

Open Fourth Congressional District Seat

How many votes do you need to win? In a race like the one going on in the Fourth Congressional District, the math becomes even more important. So does a candidate's ability to identify their base and drive them to the polls. It's not often a seat opens up for Congress in Massachusetts, and recent history has shown that when one does there's a stampede for the door. U.S. Rep. Niki Tsongas retired in 2018, leading to a 10-way primary won by Congresswoman Lori Trahan with 21.7 percent of the vote in the Third Congressional District. The situation in the western suburbs of Boston is not much different this year. Kennedy's decision to take on Markey created another opening this cycle, and the field is only slightly smaller. Nine names will appear on the ballot Tuesday, but only seven are still actively competing for the Democratic nomination, and six of those seem determined to make sure one other - Newton City Councilor Jake Auchincloss - doesn't win. Dave Cavell, a former senior advisor to Attorney General Maura Healey, and Chris Zannetos, a tech entrepreneur, both dropped out in recent weeks to back Jesse Mermell. Cavell said explicitly that part of his decision had to do with blocking Auchincloss's path to the nomination. Mermell, who led the Alliance for Business Leadership after working in Gov. Deval Patrick's administration on Beacon Hill, is considered among the top contenders for the nomination, but there has been much in the way of independent polling. Auchincloss is also a strong contender, and was endorsed by the Boston Globe, but his past identity as a Republican and comments he's made about the Confederate flag and other topics, have gotten him into hot water with his competitors and progressives. The rest of the field includes Becky Grossman, whose father-in-law Steve Grossman has been working his party contacts; City Year co-founder Alan Khazei; former Wall Street regulator Ihssane Leckey; Ben Sigel, and Dr. Natalie Linos, a Harvard University epidemiologist. Whoever prevails will be the heavy favorite in a district represented for decades by Barney Frank and then Kennedy, and will take on the winner of the Republican primary between former Attleboro city councilor and retired Air Force officer Julie Hall and Dighton Parks and Recreation Commissioner David Rosa. - Matt Murphy

Unprecedented Election Circumstances

Massachusetts held local elections this summer amid the COVID-19 pandemic, but conducting Tuesday's state primary with a large chunk of ballots submitted by mail will be an unprecedented step, and results may not come as quickly as they have in pre-pandemic elections. Through Aug. 18, about a week before the deadline, Secretary of State William Galvin's office had mailed out nearly 950,000 ballots -- representing almost a quarter of the 4.5 million registered voters in Massachusetts -- as part of a new state law allowing no-excuse mail-in voting. Lawmakers and activists warned for weeks that cuts and changes to the United States Postal Service could result in many ballots not being counted or results being muddied, prompting Postmaster General Louis DeJoy to declare in mid-August that his organization would walk back operational reforms until after the election. Even with that pledge, Galvin publicly advised all Massachusetts voters who requested mail-in ballots to submit them by hand, either to ballot drop boxes or to local election officials, to ensure they reach their destinations by the 8 p.m. deadline on Tuesday to be counted. That deadline will stand despite a challenge from Fourth Congressional District candidate Becky Grossman after the Supreme Judicial Court declined to add a 10-day extension. Election night will not look the same this time around, both because of possible delays in confirmed results and because of ongoing precautions against the lingering coronavirus. For decades, candidates, party leaders and supporters have convened at parties to watch results come in and celebrate -- or commiserate -- the outcomes, but indoor gatherings larger than 25 people remain banned under a Gov. Charlie Baker order aimed at ensuring public health. - Chris Lisinski

Voters Likely Picking Seven New House Members

In seven districts where incumbent lawmakers are not seeking re-election, the only candidates on the ballot are Democrats, so barring the rare successful write-in campaign, the winners will effectively be decided in the primary election:

-- 12th Suffolk District: In a tie for the most crowded legislative primary this cycle, three candidates are running for the 12th Suffolk District after a fourth dropped out. Mattapan attorney Stephanie Everett will aim for a return to Beacon Hill, where she worked for Sen. Sonia Chang-Diaz and former Gov. Deval Patrick before leaving for her private practice. One of her opponents, Jovan Lacet, is also an attorney and a former Boston Police Department officer, while the third, Brandy Flukey Oakley also comes from the field of law, where she worked as a public defender after spending years as a public school teacher. Oakley leads in fundraising with more than $60,000 raised compared to Everett's $40,000 and Lacet's $24,000, and Oakley also has the backing of the Massachusetts Teachers Union, Sunrise Movement and other organizations. A fourth candidate, Cameron Charbonnier, is on the ballot, but suspended his campaign in July. Charbonnier, a white man, reportedly said at the time that it is "not my moment" and that any of the other three candidates, who are Black, should instead represent a district that is roughly three-quarters people of color. The district is currently represented by Dan Cullinane, who is not seeking re-election.

-- 14th Suffolk District: Former Boston mayoral candidate Rob Consalvo is outpacing the other candidates running, counting more than $102,000 in donations with $32,700 spent. Consalvo, who lost in the 2013 preliminary election for the city's top spot, is running to succeed Rep. Angelo Scaccia. Attorney Gretchen Van Ness, who counts endorsements from a range of sitting lawmakers, Progressive Massachusetts, and the Massachusetts Women's Political Caucus, also has a sizable fundraising base for the campaign, with $69,000 raised so far and $27,000 spent. The third candidate in the race is Duckens Petit-Maitre, a law school student who has worked as an MBTA operator, a notary public, and a Boston constable. Petit-Maitre lags the other two in fundraising, with state records showing him raising $7,600 so far and committing to $11,600 in spending.

-- 16th Suffolk District: It's a two-way race in this district currently represented by RoseLee Vincent of Revere. Revere City Councilor Jessica Giannino is facing off against Joseph Gravellese, also of Revere, who has worked as an aide to Rep. Lori Ehrlich and Revere Mayor Brian Arrigo. Giannino has more than doubled Gravellese's fundraising total with $85,000 raised compared to his $30,000, while Gravellese has the backing of Progressive Massachusetts.

-- 8th Norfolk District: Two candidates are competing for the seat currently held by Rep. Louis Kafka. Ted Philips of Sharon, one of the candidates, has worked as an aide to Kafka for 13 years, currently serving as staff director. Philips is aiming to succeed his boss, citing his work on legislation related to notifying police about license suspensions, ensuring insurance coverage for children with cleft palate and cleft lip, and more. His opponent, Andrew Flowers of Walpole, is an economist and vice-chair of the Walpole Finance Committee. Flowers is running as a self-described progressive, writing on his campaign website that "Beacon Hill is stuck, spinning its wheels, when real action is needed." The two are almost evenly split in campaign funding: Philips has raised about $50,000 and spent $21,500, while Flowers has raised $51,000 and spent $20,700.

-- 5th Hampden District: Three hopefuls will face off for the seat that Rep. Aaron Vega is giving up. Holyoke's Patrick Beaudry brings seven years of experience as public affairs manager for the Pioneer Valley Planning Commission and past experience as an aide for Sen. Sonia Chang-Diaz to the race. Patricia Duffy, another Holyoke resident running for the seat, is a former publishing worker and labor leader who has received endorsements from the Massachusetts Teachers Association and other labor groups. The third candidate in the race is Holyoke City Councilor David Bartley, whose father, also named David Bartley, served as House Speaker in the 1960s and 1970s.

-- 27th Middlesex District: After unsuccessfully attempting to have her opponent tossed from the ballot, Catia Sharp will face off against Erika Uyterhoeven in a race between two Somerville Democrats. Sharp coordinates the Smart Justice Initiatives at the Middlesex County Restoration Center Commission, and she previously worked in the governor's budget office. Uyterhoeven, who describes herself as an antitrust economist and a Democratic Socialist, is a founder of the Act on Mass organization that has pushed progressive causes on Beacon Hill. Sharp's campaign filed a formal objection with the State Ballot Law Commission alleging that Uyterhoeven had not lived in the district long enough to qualify for the office, but the commission ruled in June that the complainant did not show enough evidence and allowed Uyterhoeven's candidacy to stand. This seat is currently represented by Rep. Denise Provost, who is not seeking re-election.

-- 29th Middlesex District: Three candidates are on the ballot in the House district that Rep. Jonathan Hecht of Watertown represents. Transportation consultant Steven Owens is running on a platform highlighting climate change, a statewide "transportation crisis" and affordable housing. He faces longtime Watertown Town Council President Mark Sideris, who is hoping his decades of town-level experience are appealing to voters. The third candidate in the race, David Ciccarelli, has not yet spent any money on the campaign, according to OCPF records. All three candidates live in Watertown. -- Chris Lisinski