President Barack Obama said Sunday in the race to take over his job, Republican candidate Donald Trump "proves himself unfit for this office every single day."
Obama backs fellow Democrat Hillary Clinton in the November 8 election, and spoke in support of her at an event in Las Vegas, Nevada.
Trump has in recent weeks repeatedly complained that the election process is rigged against him, something Obama said means Trump is losing.
"And, by the way, it means you don't have what it takes to do this job because there are a bunch of times where it gets tough," Obama said. "There are a lot of times where things don't go your way. And you have to be able to hang in there."
WATCH: Obama on Trump
Clinton had a similar message at a campaign event in Charlotte, North Carolina, saying that despite policy and principle differences with many previous presidents and candidates she has never before questioned whether they were fit to lead the country.
"This is not like anybody else who has ever run for president, who has demonstrated unequivocally that he is unqualified and unfit to be president and commander-in-chief of the United States of America," she said.
Trump was in Naples, Florida, Sunday where he touted his proposal to address corruption while raising questions about Clinton's conduct while in public office. Clinton has most notably faced questions about her use of a private email system during her time as secretary of state, something she has said was a mistake.
"My opponent has no plan to end government corruption because she is the embodiment of government corruption," Trump said.
He also reiterated the belief he expressed at last week's final debate that the military operation to retake the northern Iraqi city of Mosul was timed for political gain.
"The reason we went in, in my opinion, was Obama wanted to show what a tough guy he is before the election," he said.
Clinton has widened her lead in polls during the past month, including a new ABC News poll released Sunday that showed the Democrat surging to a 50-38 percent lead.
Trump has frequently questioned the validity of polls, and did so again Sunday while also repeating that the political system is "rigged."
"I'll tell you what, we're doing well in the polls, but you know I really think those polls are very inaccurate when it comes to women." Trump said. "I think we're doing better with women than with men, frankly."
Clinton told reporters traveling with her late Saturday that she plans in the final weeks of the campaign to emphasize "the importance of electing Democrats down the ballot" in an effort to try to reclaim control of Congress from Republicans.
Analysts have said Democrats stand a better chance of regaining the Senate than the House of Representatives, where Republicans hold a bigger majority.
The ABC poll said Clinton has moved to a commanding 20-point edge among female voters, 55-35, and an even bigger lead among college-educated women, 62-30. ABC also said that for the first time in its polling during the long campaign, men also favor her candidacy, 44-41. Trump is leading among white voters, still a majority of U.S. voters but a declining share of the U.S. electorate, by four percentage points, but non-whites favor Clinton by a huge margin, 68-14.
In last week's debate with Clinton, Trump's comment that “Nobody has more respect for women than I do. Nobody" drew audible laughter from the audience. Later, he interrupted Clinton to call her "such a nasty woman," a taunt that immediately has been marketed on an array of T-shirts supporting her candidacy.
Trump's plunge in national polling and key battleground election states that will determine the outcome started more than two weeks ago when a 2005 tape surfaced in which he made lewd comments about women and boasted how he could grope them because he was a celebrity. Trump later apologized and dismissed the comments as "locker room talk," and denied he had actually made unwanted sexual advances on women.
But since then 11 women have recounted instances in which he made unexpected and unwanted advances on them over several decades, all of which he said were fabrications.