"The problem is not that all Republicans think the way this guy does," the president said, noting that many Republicans have confessed to him behind closed doors to him that they're "just trying to get through this."
But, Obama said, he believes the current state of the GOP base is a result of the messages the party has been sending.
"They’ve been riding this tiger for a long time," he said. "They've been feeding their base all kinds of crazy for years."
The audience cheered as he described the environment that shapes Republican views.
"This is in the swamp of crazy that has been fed over and over and over and over again," he said. "If I watched Fox news I wouldn’t vote for me, I understand. If I was listening to Rush Limbaugh, I'd say, man this is terrible."
Trump was able to capitalize on those messages, he said, to win his bid for the GOP nomination.
"Donald Trump, as he's prone to do, he didn’t build the building himself," Obama said. "He just slapped his name on it and took credit for it, and that’s what’s happened in their party," the president went on to say.
He added that he felt many Republicans stayed quiet for years as baseless attacks were made against him, such as questions about the legitimacy of his citizenship, when their silence was politically expedient.
"Don’t act like this all started with Donald Trump," he went on to say, while adding with a chuckle, "He took it to a new level, I’ll give him credit."
Speaking to the group of Democrats, the president said he truly can't think of an election where the choice has been more clear.
"I know that folks say this every four years, but this time it's really true," Obama said. "I cannot think of a more important election in our lifetimes because the choice between two candidates has never been this stark.”
It's a choice, the president said, between someone whose as qualified as anyone has ever been for the Oval Office and someone who every day proves he’s "unfit and unqualified."
The president said he didn't need to spend much time convincing the Democratic crowd gathered to vote for Clinton. But if anyone still needed convincing, he said, they should watch his wife's speech from earlier today.
"She was pretty good," he said. "That’s why you get married, to improve your gene pool."
Being in Ohio, the president also spent some time directly contrasting Democratic Senate candidate Ted Strickland with his Republican opponent, Sen. Rob Portman.
For Republicans like Portman, who have now withdrawn their support from Trump, Obama argued, it's too late to wait until after the nominee is caught on tape making lewd remarks about women that "no decent person would say, much less brag about."
"You can’t wait until that finally happens and then say 'Oh that’s too much, that's enough,' and think that somehow you are showing any kind of leadership, and deserve to be elected to the United States Senate," he said. "You don't get points for that."
Comparing election years, Obama spoke about the differences between now and both 2008 and 2012. He said 2016 has been a "dispiriting election year" that stands in contrast with the "sense of energy and hope we felt."
He lamented the sharp divide that's come to light in this election. "I sometimes wonder 'How did we get to the point where we have such rancor?'" he said.
Though the president said there are many theories about how people became so polarized, he also noted the progress that has been made over the last eight years and expressed his optimism about the future.
"We've got to show our kids the values that we want to pass onto them," he said.