"A candidate for president of the United States should condemn violence, not encourage violence. You don't go around saying it's OK to beat people," he said. "That is not what this country is about."
The topic also opened the questioning for both Sanders and
Sanders called Trump a "pathological liar" for his assertion that Sanders' campaign had taken part in the protests.
"Our campaign … never will encourage anybody to disrupt anything," he said, adding, "I would hope Mr. Trump tones it down big time."
Clinton offered similar criticism, calling Trump's effort "a very cynical campaign pitting groups of Americans against one another. He is trafficking in hate and fear; he is playing to our worst instincts."
Sanders cited polls that show him beating Trump, in some cases by wider margins than Clinton.
When her turn came, Clinton noted that 25 years of being in public life, under attack from political opponents, has toughened her.
"Whoever goes up against Donald Trump better be ready," she said, adding that her experience as secretary of State would allow her to make the case to voters about "how dangerous a Donald Trump presidency would be … for the peace of the world."
The protests surrounding Trump have added an unpredictable component to the Republican primary race, with the three challenging candidates taking on the front-runner. For the Democrats, delight in the Republican feuding must for the moment take a back seat to the vote on Tuesday.
Polls have shown Clinton ahead in several states, including Ohio, but after Sanders eclipsed her double-digit lead to win Michigan, both campaigns presume the results are up in the air.
Clinton and Sanders have been traveling through Ohio, nearly begging voters to side with them and turn out. By this late in the season, their pitches have been honed.
For Clinton, the argument is that she shares many of the same liberal goals as Sanders but would be far better at achieving them. She spent Sunday traveling to an African American church on the outskirts of Cleveland and a bakery in Marion, Ohio, about an hour from Columbus.
There she pressed her argument that she would "break down barriers" confronting Americans.
"I'm going to do everything I can as president, if I'm so lucky as to be president, to really help people feel like the opportunities that are within their reach, again," she said at the 8 Sisters Bakery.
Sanders spoke to thousands of enthusiastic supporters during his Ohio State visit. He made his standard call for a Medicare-for-all healthcare system, free tuition for public colleges and universities, and a reversal of trade deals that he blames for 60,000 factory closings in the last 15 years.
He also reiterated his opposition to the war in Iraq, which Clinton supported as a senator from New York.
"I know it's a radical idea," he said, mocking the criticism made of him, "but maybe we want to rebuild the water system in Flint, Mich. Maybe we want to rebuild roads, bridges and rail systems rather than rebuilding the infrastructure of Iraq or Afghanistan."
Sanders will open the final day of campaigning before Tuesday's primaries in Youngstown, in northeast Ohio, before holding rallies in Ohio, North Carolina, Missouri and Illinois.
For more on Campaign 2016, follow @CathleenDecker