In this Aug. 12, 2020, file photo Democratic presidential candidate former Vice President Joe Biden and his running mate Sen. Kamala Harris, D-Calif., pass each other as Harris moves tot the podium. (AP Photo/Carolyn Kaster, File)

President Donald Trump questioned former Vice President Joe Biden’s mental capabilities and mocked Sen. Kamala Harris of California as an extreme liberal in three campaign rally-like appearances Monday as Democrats began their four-day national political convention nominally in Milwaukee but largely online.

Standing in front of Air Force One in Wisconsin, a state that delivered 10 critical electoral votes for the president’s 2016 victory over Hillary Clinton, Trump warned that the 2020 election was a “fight for the survival of our nation and civilization itself” and condemned Biden as a puppet of the “radical left” in the Democratic Party.

“You want to crush our economy,” Trump asked the crowd at the Oshkosh airport, “under the crazy socialist policies of sleepy Joe Biden and his boss, Kamala Harris — Kamala — and his other boss, Nancy Pelosi — she’s a beauty — and his ruler, Bernie Sanders, crazy Bernie, or do you want to quickly rebuild the strongest economy in the history of the world?”

Trump’s reelection campaign has struggled to get traction amid the coronavirus pandemic that has devastated the nation’s economy and forced cancellations and shutdowns across vast swaths of American life. The president’s early dismissals of the threat from the virus, and his administration’s chaotic response, have helped drive some of his poll numbers down to double-digit deficits against Biden.

Trump pointedly chose Oshkosh, not far from Milwaukee, in an attempt to counterprogram four days of speeches from Democratic Party stars and some Republicans who have soured on Trump.

At a stop earlier Monday in Mankato, Minnesota, Trump delivered an hourlong speech to a small crowd at the airport, accusing Biden of wanting to raise taxes, weaken police departments, open borders, increase the cost of energy and lock people in their homes because of the pandemic.

“He will kill the stock market,” Trump said. “He will kill everything that we’re talking about today. You’d also abolish immigration enforcement, abolish bail, abolish the suburbs, abolish effective policing, abolish American energy and abolish the American way of life.”

Earlier in his remarks, he boasted about having done an “incredible” job confronting the spread of the virus and falsely said Biden wanted to “lock all Americans in their basements for months on end, which would inflict permanent irreversible harm on our nation’s children, families health and economy.”

Trump’s first stop of the day was at the airport in Minneapolis, where there were protests and violence after the death of George Floyd at the hands of a police officer in the city. Trump lashed out at Biden and other Democrats for enabling what he called “radical left anarchists” who looted parts of Minneapolis.

“Everyone says, ‘Oh, don’t use that term, radical left,’ ” Trump said. “I go ‘radical left anarchists!’ ”

Before Trump’s arrival in Minnesota, Tim Walz, the state’s Democratic governor, said Trump had wanted to make his remarks in front of a memorial to Floyd. Walz said he had “spent this weekend trying to tell the White House why it was a really bad idea” to use it as a backdrop for Trump’s campaign.

White House officials said Walz was mistaken. “Who did you reach out to at the White House?” Judd Deere, a White House spokesman, said in a tweet. “Nobody here heard from you. @realdonaldtrump would never use the George Floyd Memorial as a political backdrop, but he does want to hear from business owners impacted by the riots.”

Trump began his day with an early-morning critique in a Fox News interview suggesting that Biden’s mental capacity was lacking.

“Biden is shot. I’m telling you he’s shot. There’s something going on,” the president said. “Now with that being said, I don’t underestimate anybody. Only a fool would do that.”

Trump and his campaign have repeatedly insinuated — without any evidence — that Biden is mentally slow.

In the same interview, Trump called Harris “a disaster” and then misstated her positions by saying that “she wants to take away everyone’s gun. She wants to totally ban fossil fuels.” The president shrugged off a question about whether he is preparing for the upcoming debates against Biden, saying that he did not prepare much for the debates he participated in during the 2016 presidential campaign.

“Honestly, what I’m doing is I’m doing my job,” he said, adding: “I mean that’s the best debate prep. I’ve sort of been preparing all my life. That’s what I do. I guess I’ll do some preparation, but I didn’t do much last time.”

In Oshkosh, a few blocks from the airport, Kylie Burk, 19, of Fond du Lac, Wisconsin, was selling Trump merchandise in the parking lot of an auto lube shop, including Confederate flag caps.

Burk said the Confederate caps were “popular — we supply what people want.” Asked if she thought it was a good idea to associate Trump with a racist symbol, she said, “I don’t believe the Confederate flag stands for racism, and that’s all I’m going to say about that.”

Burk said she plans to vote in her first presidential election for Trump because “I like his ideas and the very good things he’s doing for our country.”

“Before COVID, the unemployment rate was at an all-time low and jobs were at an all-time high,” she added.

At the Winnebago County Democrats’ office in downtown Oshkosh, Kathy Zuehlsdorf said that the phone had been ringing off the hook all day and that people were coming in to pick up Biden lawn signs.

Former President Barack Obama won Winnebago County in 2008 and 2012, but in 2016 the county flipped Republican in a close election as Trump narrowly won the state. Democratic officials in the county said they were optimistic this year.

“We have gone through hundreds of Biden signs, and we’re ordering 400 more,” Zuehlsdorf said.