That leaves Biden in the position of holding a consistent lead in the national polls and an advantage in most battlegrounds, including Michigan, yet still facing anxiety it could all slip away.
As of Saturday morning, nearly 90 million voters had already cast ballots nationwide, according to a tally by The Associated Press.
Tens of millions more will vote by the time polls close on Tuesday night.
Obama said he initially hoped "for the country's sake" that Trump "might take the job seriously. He never has."
The former president, addressing voters in dozens of cars in a Flint high school parking lot, seized on Trump's continued focus on the size of his campaign crowds.
"Did no one come to his birthday party when he was a kid? Was he traumatized?" Obama mocked.
"The country's going through a pandemic. That's not what you're supposed to be worrying about."
Trump made an aggressive play for pivotal Pennsylvania, focusing largely on his white, working-class base.
His first of four scheduled stops in Pennsylvania was in a small town in Bucks County on the eastern edge of the state.
Repeating what has become a consistent part of his closing message, Trump raised baseless concerns about election fraud, pointing specifically at Philadelphia, a city whose large African American population is key to Biden's fate in the state.
"They say you have to be very, very careful what happens in Philadelphia," Trump charged. "Everybody has to watch."
The president also railed against a recent Supreme Court ruling that will allow Pennsylvania to count mail ballots received as many as three days after polls close.
The extra time, Trump alleged without evidence, would allow for fraud and potentially deny him a win in the state. "What's going on?" he asked during a late afternoon rally in Reading, Pennsylvania.
"That was a very disappointing opinion, but I've had many disappointing opinions from the Supreme Court."
Several studies, including one commissioned by Trump himself, have failed to uncover any significant examples of election fraud.
Good-government advocacy groups are concerned that the president's repeated calls for his supporters to monitor the polls may lead to widespread voter intimidation.
Republicans are betting that Trump can win a second term by driving up turnout among his strongest supporters white, noncollege-educated men and rural voters while limiting Biden's advantage with Blacks and Latinos.
Democrats in several swing states worry that voters of colour may not be excited enough about Biden to show up in the numbers they need.
In Michigan, Rep. Dan Kildee, a Democrat who represents the Flint area, said he had been pressing for a couple of months for Biden or Obama to visit the majority Black city where a water crisis that began in 2014 sickened the city's residents, exposing stark racial inequities.
"Showing up matters," Kildee said.
"The message is important, no question about it. But there's a message implicit in showing up, especially in Flint. This is a community that has felt left behind many, many times and overlooked many, many times."
R&B legend Stevie Wonder was to perform in Detroit after Biden and Obama speak.
Biden's campaign announced it was sending Obama to Florida and Georgia on Monday. He is the campaign's most valuable asset to help energize the nonwhite voters Democrats so badly need to defeat Trump.
"Joe Biden is my brother. I love Joe Biden, and he will be a great president," Obama said Saturday.
The press for Michigan's Black voters comes after voting was down roughly 15 per cent in Flint and Detroit four years ago a combined 48,000-plus votes in a state Trump carried by about 10,700 votes.
Overall, the Black voter turnout rate declined for the first time in 20 years in a presidential election, falling to 59.6 per cent in 2016 after reaching a record-high 66.6 per cent four years earlier, according to the Pew Research Center.
Trump isn't ceding Michigan to Biden.
He visited Waterford Township, near Detroit, on Friday and held a rally in the state capital, Lansing, this past week, though the surging coronavirus cases are clouding his presidency.
The worst week of the year, in terms of new infections, arrived with Election Day looming.
More than 99,000 Americans reported new infections on Friday, a record high, according to Johns Hopkins University.
Trump told Pennsylvania voters that his administration has done "an incredible job" dealing with the pandemic.
He promised that the mass distribution of a vaccine was "just weeks away.
(Only the headline and picture of this report may have been reworked by the Business Standard staff; the rest of the content is auto-generated from a syndicated feed.)
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