WEST CHESTER, Ohio — Unsettled by images of violence and ugliness at Donald J. Trump's rallies, the Republican leaders pushing to stop him are desperately targeting voters in the five big states that vote on Tuesday.

The weekend of disturbances at Mr. Trump's rallies injected more unease into the race, and the appeals of his rivals turned emotional and urgent. On Sunday, Senator Marco Rubio of Florida warned that a Trump White House would exploit hatred and stir violence. "Imagine what that means for the country," Mr. Rubio said. "Imagine the tone it sets for our culture."