Democrats brought their firepower to Michigan, a critical swing state that helped seal President Trump's 2016 victory. 

Former Vice President Joe Biden and former President Barack Obama made their first joint 2020 campaign stop on Saturday afternoon in Flint before heading to Detroit. They hit Trump hard on his handling of the coronavirus pandemic and said it's time to restore decency to the White House.

During the Obama Biden Halloween campaign stop Saturday, they were joined by Motown legend Stevie Wonder, whose “Signed, Sealed, Delivered” became an anthem of sorts for the Obama campaign in 2008. 

Obama took to the stage first Saturday night to throw his backing behind Democratic presidential nominee Joe Biden. "The presidency doesn't actually change who you are, it just reveals who you are," Obama said.

"Look, I knew Donald Trump wasn't going to agree with me. But I did think he was going to take it seriously."

Trump hasn't, in his opinion, Obama said.

He accused Trump of being "jealous" of COVID's media coverage and condemned Trump's accusations that doctors were "profiting" from the virus. 

The former president said that manufacturing grew in Michigan during their final four years in office by 15%, in comparison to the 1% of growth during Trump's four-year term. 

Obama turned his speech to health care and criticized Republicans' efforts to repeal the Affordable Care Act without the alternative plan they've "promised for 10 years."

Obama then turned to Trump's character. If a "coworker lied everyday...we would fire him," adding that voters would not have to worry about Biden's ability to tell the truth. 

Biden took to the stage and said, "thank you for reminding us what we can be again," then condemned Trump as a leader.

"Three days we can put an end to a president that has failed to protect this nation," Biden said. "I don't care how hard the president tries, there's nothing he can do to prevent the people from voting."

Biden pointed to the 9 million U.S. cases of coronavirus and over  230,000 deaths. He claimed, "he lied to the American people, he knew it wasn't going to disappear."

Biden jumped in on manufacturing and wealth, and said that people who make less than $400,000 will not pay more taxes, but added that the wealthy need to start paying their "fair share."

"Why should you all be paying more in taxes than Donald Trump, the millionaire?"

"Well, guess what Mr. President, I'm coming for you," Biden added. 

Biden went on questioning Trump's "courage," saying he is unfit to lead the servicemen and women who he has disparaged in the past.

“I’m running as a proud Democrat, but I will govern as an American,” Biden said.  

Earlier that day, in Flint, he told supporters, "It's time for Donald Trump to pack his bags and go home."

"We're done with the chaos, the tweets, the anger, the hate, the failure [and] refusing to take any responsibility."

Democratic presidential candidate former Vice President Joe Biden, right, and former President Barack Obama wave to the audience at a rally at Northwestern High School in Flint, Mich., Oct. 31. (AP Photo/Andrew Harnik)

Democratic presidential candidate former Vice President Joe Biden, right, and former President Barack Obama wave to the audience at a rally at Northwestern High School in Flint, Mich., Oct. 31. (AP Photo/Andrew Harnik)

Biden thanked Obama for being a "great" president and suggested a Biden presidency would be free of scandal. Biden has dismissed recent allegations that his son, Hunter, involved him in foreign business dealings.

"[We] went through eight years without one single trace of scandal ... It's gonna be nice to return to that," Biden said.

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Both Obama and Biden went after Trump for claiming in Michigan Friday that doctors purposely inflate coronavirus death numbers to make money.

"What in the hell is wrong with this man?" Biden said.  "Excuse my language, but think about it -- it's perverted. He may believe it because he doesn't do anything other than for money."

COVID-19 cases in the United States reached a record high on Friday. But at a rally in Waterford, Mich., Friday, Trump seemed to blame doctors for the surging coronavirus numbers in the United States.  

Democratic presidential candidate former Vice President Joe Biden speaks at a rally, also attended by former President Barack Obama, at Northwestern High School in Flint, Mich., Oct. 31. (AP Photo/Andrew Harnik)

Democratic presidential candidate former Vice President Joe Biden speaks at a rally, also attended by former President Barack Obama, at Northwestern High School in Flint, Mich., Oct. 31. (AP Photo/Andrew Harnik)

"Our doctors get more money if somebody dies from COVID. You know that, right? I mean our doctors are very smart people. So what they do is they say, 'I'm sorry, but everybody dies of COVID,'" Trump said.

Trump's comments were quickly denounced by the American Medical Association (AMA) as outrageous.

Obama has been campaigning in battleground states for Biden, but Flint is the first time they campaigned together during the final stretch, signifying the importance of winning Michigan. 

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"Joe Biden is my brother. I love Joe Biden, and he will be a great president," Obama said in his speech before Biden took the stage.

Obama ripped into Trump's handling of the growing coronavirus pandemic and accused the president of holding superspreader rallies because of his obsession with big crowds.

"Trump cares about feeding his ego," Obama said. "Joe cares about keeping you and your family safe."

Obama and Biden have developed goodwill in Michigan for efforts to save the auto industry at a time when Republicans, like 2012 GOP presidential nominee Mitt Romney, penned an op-ed titled: "Let Detroit go Bankrupt." Obama compared GOP efforts to turn their backs on the auto industry to Trump's "botching" of the pandemic response and suggested the new GOP slogan is: "Let America get COVID."

Former President Barack Obama speaks at a rally for Democratic presidential candidate former Vice President Joe Biden, at Northwestern High School in Flint, Mich., Oct. 31. (AP Photo/Andrew Harnik)

Former President Barack Obama speaks at a rally for Democratic presidential candidate former Vice President Joe Biden, at Northwestern High School in Flint, Mich., Oct. 31. (AP Photo/Andrew Harnik)

Trump, campaigning in Pennsylvania on Saturday, hit back on Biden and Obama by trying to link them to the Flint water crisis and accepting the endorsement of former GOP Gov. Rick Snyder who was in office when lead from aging pipes leached into Flint's water supply. State and local officials in Michigan were charged with crimes related to the contaminated water, though charges against eight of those people have since been dismissed.  

"Biden & Obama owe a massive apology to the People of Flint," Trump tweeted. "The water was poisoned on their watch. Not only did they fail them, Biden proudly accepted the endorsement of disastrous Gov Rick Snyder! Unlike Biden, I will always stand with the People of the Great State of MICHIGAN!"

If Biden wins Michigan, it would be a blow to Trump's path to reelection. Trump stunned the world in 2016 by flipping three traditionally blue states --- Michigan, Wisconsin and Pennsylvania --  and he is staking another four years in the White House on repeating his Midwest success. 

Michigan is also a big battleground state for the Senate, where Sen. Gary Peters, D-Mich., is trying to fend off a challenge from Republican Army veteran John James. Peters joined Biden and Obama on Saturday and stressed the importance of Democrats coming out to vote. 

Trump has been stumping hard in Michigan with a rally Friday in Waterford Township. He plans to return on Sunday and Monday in his closing rally blitz.

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The night before the election in 2016, Trump's final campaign rally went past midnight in Grand Rapids, Mich. Hoping to repeat history, the Trump campaign says the president’s last stop in the 2020 race will be Grand Rapids.

President Donald Trump speaks at a campaign rally at Oakland County International Airport, Oct. 30, in Waterford Township, Mich. (AP Photo/Jose Juarez)

President Donald Trump speaks at a campaign rally at Oakland County International Airport, Oct. 30, in Waterford Township, Mich. (AP Photo/Jose Juarez)

Democrats are trying to leave nothing to chance this time around and are pushing for a strong turnout. 

"We got a little complacent in the last election," Obama acknowledged Saturday in Flint. 

Biden says he has learned from the mistakes that Clinton’s campaign made four years ago in the Midwest.

Clinton was criticized for not campaigning enough in Midwestern states like Wisconsin and Michigan. After her stunning loss in 2016, many Democrats criticized her campaign as overconfident and too complacent.

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In contrast, Biden often insists he’s taking no vote for granted and said Friday night in Wisconsin, “I’ve been here a lot.” 

Fox News' Paul Steinhauser and The Associated Press contributed to this report.