PHILADELPHIA (AP) — Joe Biden is adopting an increasingly aggressive stance as he looks to break out of a monthslong campaign freeze imposed by the coronavirus outbreak.

Over the course of 24 hours, the presumptive Democratic nominee stepped up his rhetoric against President Donald Trump, warning he could try to steal the election. His campaign organized a petition pressing Facebook to boost its efforts to prevent the spread of misinformation. And he released a plan to restart an economy crippled by the coronavirus in a way that he says won't make Americans choose between their health and livelihoods.

The quick succession of developments was a signal of Biden's growing desire to become more assertive on multiple fronts. He's betting that he can build momentum by offering a contrast to Trump's leadership as the country is gripped by the pandemic, economic turmoil and unrest stemming from racial injustice and police brutality.

“Trump has basically had a one-point plan: Open businesses,” Biden said Thursday at an economic roundtable in Philadelphia, where he announced a plan to reopen the economy. “It does nothing to keep workers safe, to keep businesses able to stay open, and secondly it does very little to increase consumer confidence.”

If elected, Biden promised, among other things, to guarantee testing and protective equipment for people called back to work while prohibiting discrimination against elderly Americans and anyone else who is at high risk of contracting the virus. He also wants to use federal funds to ensure paid leave for anyone who falls ill or cares for those who do.

He proposed a national contact tracing workforce or “job corps” of at least 100,000 to call people who test positive, track down their contacts and get them into quarantine. That figure — at least 100,000 — aligns with an estimate from the Johns Hopkins Center for Health Security and the Association of State and Territorial Health Officials. Health experts agree that contact tracing is crucial to slowing the spread of the virus and that there aren’t enough public health workers today to achieve what’s needed.

Biden also backed more funding for schools and child care centers as they reopen and the creation of a “safe shopper” program meant to make returning consumers less wary of getting sick as life begins returning to normal.

He referenced the potentially eye-popping price tag of such ambitious plans, joking, “There goes that big spending Democrat again." But Biden added: “If we don’t do this, we’re going to be in deep, deep, deeper trouble economically.”

As the plan was being released, his campaign circulated an online petition urging Facebook to strengthen its misinformation rules. Social media giant Twitter has already drawn Trump's ire by imposing stricter limits on how he and others use the social media network.

“We’re sending Facebook a letter demanding that the company change its policies to crack down on misinformation in ads and ensure a fair election,” the petition reads. Facebook responded that “the people’s elected representatives should set the rules, and we will follow them.

“There is an election coming in November and we will protect political speech,” the company said in a statement "even when we strongly disagree with it.”

As his campaign strikes at Facebook, Biden is also dramatically increasing spending on the platform. His campaign outlaid millions of dollars on ads that are themed around the protests sweeping the country and Trump’s response to them.

After remaining at home for months, Biden has begun holding public events within driving distance of his house in Delaware. But his more aggressive approach has so far not extended to resuming large campaign rallies.

That is in contrast to Trump, who flew to Dallas on Thursday for a $10 million fundraiser and says he’ll begin holding a series of rallies starting next week in Oklahoma. Biden’s campaign says it will resume normal campaign travel and events when public health officials and authorities say it's safe.

Melissa Reed, a spokesperson for Trump Victory in Pennsylvania, said voters “don’t want to return to the stagnant economic growth under the Obama-Biden Administration, they want a Great American Comeback under President Trump.”

Biden's economic plan and Facebook criticism followed him saying his chief worry is that Trump will attempt to “steal” November's election — and that he's even considered the possibility that the president would refuse to leave the White House should he lose.

“My single greatest concern: This president’s going to try and steal this election,” Biden said on “The Daily Show with Trevor Noah,” which aired Wednesday night. “This is a guy who said all mail-in ballots are fraudulent, voting by mail, while he sits behind the desk in the Oval Office and writes his mail-in ballot to vote in the primary.”

Biden was asked whether he’s considered what would happen if Trump refused to vacate the presidency in the event he wasn’t reelected. “I have,” the former vice president responded, before suggesting that the military could step in to ensure a peaceful transition of power.

“I am absolutely convinced they will escort him from the White House with great dispatch,” Biden said.

White House press secretary Kayleigh McEnany responded that Biden was taking “a ridiculous proposition.”

Trump has intensified his claim that absentee voting, which many states are expanding to avoid large crowds at polling places during the coronavirus outbreak, increases the possibility of fraud. There is little evidence to support that assertion, and Trump himself has voted by mail in the past.

Still, a chaotic Tuesday primary in Georgia, where there were problems with voting machines and long lines, may foreshadow a messy November election. Biden said on the “Daily Show” that his campaign would hire lawyers to observe balloting in "every district in the country.”

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Weissert reported from Washington. Associated Press writer Carla K. Johnson in Washington state contributed to this report.