President Barack Obama waded into the nation's fractious White House campaign on Saturday, calling on candidates to steer clear of the incendiary language that has coarsened the tone of the battle to succeed him.

"What the folks who are running for office should be focused on is how we can make it even better -- not insults and schoolyard taunts and manufacturing facts, not divisiveness along the lines of race and faith, certainly not violence against other Americans," Obama said at a fundraiser in Dallas, Texas.

He was speaking one day after a Chicago rally organized by Republican frontrunner Donald Trump had to be called off amid violent clashes between his supporters and protesters.