AFP / JIM WATSON Alabama Republican candidate Roy Moore was seen as a shoo-in for a US Senate seat, but allegations that he had molested minors have dealt a blow to his campaign

Candidates in Alabama's intensely-watched Senate race made their final pitches to voters late Monday, after President Donald Trump urged loyalists to elect the firebrand Republican Roy Moore despite accusations he molested minors decades ago.

The two protagonists in the race, Moore and Democrat Doug Jones, headlined competing rallies where they implored their supporters to march to the polls and vote Tuesday, on perhaps the most closely watched US election day of 2017.

"Everyone in this state -- and most of the people in this nation -- are watching this election," Moore told a few hundred people at his first public campaign event in six days, as he blasted the outside influence on the race.

The election appeared headed to the wire in this conservative bastion and unexpected battleground, where energized Democrats pulled out the stops, recruiting Barack Obama to rally support for the party's standardbearer.

"This one's serious. You can't sit it out," the former president says in a robocall ahead of Tuesday's special election. "So get out and vote, Alabama."

Trump has put out a call of his own, telling residents that "I need Alabama to go vote for Roy Moore."

Until recently it had been unimaginable for a Republican to lose a statewide election in Alabama, which Trump carried handily and which has not elected a Democrat to the Senate since 1992.

But Moore's candidacy turned toxic for the Republican Party after The Washington Post published an investigative account including accusations by women who claim he sexually molested or pursued them when they were in their teens and he was a state attorney in his thirties.

One of the women says she was 14 when Moore molested her. Moore, now 70, denies the allegations.

Some in the Republican establishment have sought to distance themselves from Moore. But with Republicans clinging to a razor thin Senate majority, Trump -- who himself was infamously caught on tape boasting about groping women -- has given Moore his political blessing.

- 'They're coming for you' -

The latest survey by Fox News put the Democrat Jones ahead by 10 points, although a new Emerson poll has Moore ahead by nearly that much. The two are competing to replace Jeff Sessions, who become US attorney general.

Moore was a controversial figure even before the latest allegations against him: twice elected chief justice of Alabama's Supreme Court, he was twice dismissed from the post, first in 2003 for refusing to remove a Ten Commandments statue from the court house.

In 2016, he defied the US Supreme Court by refusing to apply its decision legalizing same-sex marriage.

It's a pragmatic alliance between the US president's economic populism and Moore's religious activism.

Stephen Bannon, the former White House strategist who proclaimed himself the guardian of the Trump revolution, appeared alongside Moore at a final "Drain the Swamp rally," where Moore's team had installed fake alligators in a makeshift swamp.

"They're coming for you," he warned the crowd, speaking of establishment lawmakers in Washington. "They're trying to shut you up."

GETTY IMAGES NORTH AMERICA/AFP / JUSTIN SULLIVAN Democrat Doug Jones of Alabama has a stiff challenge against Republican Roy Moore in their battle for a US Senate seat

Until Monday Moore had been nearly invisible this past week apart from his flood of TV campaign ads, perhaps to avoid the swirling controversy about his past.

- State before party -

For the Republican majority in Washington, the election is a loser in every way. Should Moore prevail, party leaders fear being soiled by association. Should he lose, their thin Senate majority of 52 out of 100 seats will shrink to 51, allowing Trump virtually no room for maneuver.

Yet if Moore wins, it could spell campaign gold for Democrats heading into next year's mid-term elections, admits Senate Republican Lindsey Graham.

"Roy Moore will be the gift that keeps on giving for Democrats," Graham told CNN.

Jones, 63, is a former federal prosecutor known for having convicted two Ku Klux Klan members for bombing a black church in Birmingham, killing four African-American girls.

To win, he will need to mobilize the Democratic base, including the black community that Obama targeted with his robocall.

"This election is going to be one of the most significant in our state's history," Jones told a cheering crowd in Birmingham.

"It is time that we put our decency, our state, before a political party."

A Jones victory would likely need crossover votes from Republicans. But his support for abortion rights is anathema to many conservatives, who may choose to write in another candidate aside from the two on the ballot.

Polls in Alabama remain open from 7:00 am to 7:00 pm Tuesday (1300 to 0100 GMT)