President Obama offered a full-throated endorsement of Hillary Clinton Hillary Diane Rodham ClintonJoe Biden looks to expand election battleground into Trump country Biden leads Trump by 12 points among Catholic voters: poll The Hill's Campaign Report: Biden goes on offense MORE’s fitness to serve as president on Tuesday, two days after she suffered a health scare that roiled her campaign.

“You want to debate who’s more fit to be our president?” Obama asked a Philadelphia crowd during a his first solo campaign appearance for Clinton.

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“We have one candidate who’s traveled to more countries than any secretary of State ever has, has more qualifications than pretty much anyone who has ever run for this job,” he continued.

Obama said that Republican nominee Donald Trump Donald John TrumpBubba Wallace to be driver of Michael Jordan, Denny Hamlin NASCAR team Graham: GOP will confirm Trump's Supreme Court nominee before the election Southwest Airlines, unions call for six-month extension of government aid MORE, by comparison, “isn’t fit in any way shape or form to represent this country abroad and be its commander in chief.”

The president defended Clinton’s stamina to serve in the nation’s highest office, which her critics have questioned after her pneumonia diagnosis was revealed on Sunday.

“She worked hard, tirelessly flying around the world again and again,” he said. “I don’t know how many times she lapped the world but she did it a long time.”

Speaking at the foot of the steps at the Philadelphia Museum of Art, famously depicted in the “Rocky” movies, the president likened his 2008 Democratic primary campaign against Clinton to the fictional boxer’s run up the stairs.

“I was about to celebrate and then I look and she’s right there,” he said, adding that Clinton “whupped” him in the Pennsylvania primary. “It was tough, because Hillary’s tough.”

The Clinton campaign has been focused on damage control since video surfaced Sunday showing her needing help to get into a car after leaving a 9/11 memorial ceremony early.

Many have questioned how the campaign handled the incident and questioned whether the pneumonia diagnosis made Friday would ever have been revealed had Sunday’s near-collapse not been caught on camera.

Obama bemoaned media coverage of transparency issues that he said has been too favorable to Trump, ripping him for refusing to release his tax returns like other past presidential nominees.

"You want to debate transparency?" he asked. "You've got one candidate in this race who's released decades worth of her tax returns. The other candidate is the first in decades who refuses to release any at all."

The Clinton campaign has promised to release more detailed health records later this week, and the Democratic presidential nominee is expected to be back on the campaign trail soon.

With Clinton recuperating at home, Obama sought to reset the tenor of the debate with a forceful, energetic speech that lavished praise on his preferred successor.

“I am really into electing Hillary Clinton,” he told the crowd, which numbered more than 6,000, according to the Clinton campaign. “This is not me going through the motions here. I really, really, really wanna elect Hillary Clinton.”

Obama used his platform in the City of Brotherly Love to launch into one his most blistering critiques yet of Trump.

The president dismissed the Republican nominee’s effort to position himself as a working-class hero.

“Really, this is the guy you want to be championing working people?” he asked. “This guy, who spent the first 70 years of his life showing no concern for working people?

“I mean, he wasn’t going to let you on his golf course,” he added. “He wasn’t going to let you buy in his condo. And now suddenly this guy is going to be your champion?”

And Obama mocked Trump’s praise for strongmen like Russian President Vladimir Putin.

“He loves this guy,” he said. “Think about the fact that that is Donald Trump's role model. I have to do business with Putin, I have to do business with Russia. That's part of foreign policy, but I don't go around saying that's my role model.”

He also blasted Trump and his fellow Republicans for peddling a “dark, pessimistic vision” of the country during the presidential campaign.

“They're not offering serious solutions,” he added. “They're just fanning resentment and blame and anger and hate.”

Obama is seeking to fire up voters in the Keystone State, a traditional Democratic stronghold where the race between Clinton and Trump has narrowed in recent weeks.

A new Quinnipiac University poll showed the Democrat holding only a five-lead over her Republican opponent there.

If Clinton defeats Trump in Pennsylvania, a state Democrats have won in each presidential contest since 1988, it could prevent the businessman from winning enough electoral votes to claim victory in November.

Some Democrats are concerned about an enthusiasm gap between Clinton and Trump supporters in places like Pennsylvania, and the president implored voters to get to the polls in eight weeks.

“Democracy is not a spectator sport,” he said. “You don't tweet in your vote.”

Obama’s spirited demeanor underscored how much his presidential legacy is tied to the former secretary of State’s success or failure.

As he walked off the stage, the president slapped the side of the podium three times after imploring the crowd to “get busy” campaigning for Clinton.

The president ticked off a list of his administration’s accomplishments, including new Census data showing across-the-board declines in the poverty rate and rising incomes in 2015.

He joked to an audience member who shouted out $2 gas, “thanks for reminding me. Thanks, Obama.”

And he said the prospect of Trump’s election in the fall presents a “fundamental choice about who we are as a people.”

“The choice that we make just eight weeks from today will determine the direction of this country for a long time,” he said.