US President Barack Obama has mounted a vigorous defence of Hillary Clinton, her campaign's transparency and her fitness for the presidency, and accused Republicans of fanning "anger and hate".
Mr Obama painted a stark picture of the stakes in the face-off between Mrs Clinton and Republican rival Donald Trump, and tried to persuade Democrats that he is fully behind his former secretary of state's bid for the White House.
"Hillary Clinton is steady and she is true," Mr Obama told a group of cheering Democrats at an outdoor rally. "I need you to work as hard for Hillary as you did for me."
Mr Obama aggressively stepped into a void left by Mrs Clinton, who is taking time off from campaigning after being diagnosed with pneumonia.
Mr Obama is seeking to generate momentum for Mrs Clinton in a race that has become uncomfortably close for many Democratic supporters. The latest poll by Quinnipiac University found her with a five percentage-point edge over Mr Trump in Pennsylvania.
Mr Obama's campaign appearance at an outdoor plaza in front of the Philadelphia Museum of Art was his third for Mrs Clinton, including his speech at the Democratic National Convention. The president, who remains broadly popular among the Democratic base, is viewed as a key asset in pushing die-hard Democrats to the polls.
But the president's day job has kept him from being a fixture. Mr Obama recently returned from 10 days abroad in Asia and will attend a United Nations meeting next week, leaving him just six weeks of full-throttle campaigning for Mrs Clinton.
Mr Trump's campaign, meanwhile, responded to Mr Obama's appearance with a statement suggesting he was shirking his duties.
"Shouldn't you be at work?" it read. "President Obama would rather campaign for Hillary Clinton than solve major problems facing the country."
At the rally, Mr Obama made both the case for Mrs Clinton and for his own presidency.
He claimed successes on diplomacy, health care, winding down the war in Afghanistan and reviving economy, which showed new strength on Tuesday in a Census report documenting a jump in household incomes in 2015.
"Republicans don't like to hear good news right now but it's important to understand this is a big deal," Mr Obama said of the new report, later joking: "Thanks, Obama."
The candidate whom Mr Obama hopes will succeed him left a 9/11 ceremony after about 90 minutes on Sunday and struggled to stay on her feet while she was helped into a van.
Mrs Clinton's campaign said she had "overheated", but later revealed that she had been diagnosed on Friday with pneumonia. The episode played into Mr Trump's efforts in recent weeks to raise doubts about Mrs Clinton's stamina.
Mrs Clinton's campaign was already on the defensive after she used the term "basket of deplorables" to describe half of Mr Trump's supporters.
White House spokesman Josh Earnest said Mr Obama does not feel like he needs to help Mrs Clinton with damage control.
"I think the president's belief that she'd be an excellent president of the United States is something that you've heard him say many times. And I can tell you there's nothing that happened yesterday that has changed that assessment at all," Mr Earnest said.