Speaking at a campaign rally in Greensboro, North Carolina, for Democratic presidential nominee Hillary Clinton, Obama said the choice was clear in the Nov. 8 election even before the tape was leaked last week showing Trump speaking crudely about women.
"Now you find a situation in which the guy says stuff that nobody would find tolerable if they were applying for a job at 7-Eleven," Obama told the crowd, referring to the convenience store chain.
Trump said during Sunday night's presidential debate he was embarrassed by the video, but dismissed it as "locker room talk."
Obama also criticized some Republicans who have condemned the remarks but are still backing the New York businessman.
"The fact that now you've got people saying: 'We strongly disagree, we really disapprove ... but we're still endorsing him.' They still think he should be president, that doesn't make sense to me," Obama said.
Earlier on Tuesday, White House spokesman Josh Earnest said the remarks in the recording amounted to sexual assault.
Obama also took aim at Trump's business credentials, referring to a New York Times report that showed he claimed a nearly billion dollar loss in one year on his taxes in the 1990s.
"They say the house always wins," Obama quipped about Trump, who was a casino developer at the time. "I don't know how that happens.