Republican US presidential candidate Ted Cruz hugs running-mate Carly Fiorina just before announcing that he is suspending his campaign for president at a campaign event during Indiana primary night in Indianapolis, Indiana, US, May 3, 2016. [Photo/Agencies]

Campaigning in Evansville, in the state's southwest corner, Cruz sounded deeply frustrated by the bombastic real estate mogul, who has ripped Cruz at every turn.

"The man cannot tell the truth but he combines it with being a narcissist," Cruz said, "a narcissist at a level I don't think this country has ever seen."

Cruz termed Trump a "serial philanderer" - likely as part of his strategy to try to win the support of evangelical voters. Trump, in response, said Cruz had become "more and more unhinged."

The only hope Kasich has for becoming the Republican nominee is to somehow deny Trump the 1,237 delegates he needs to win the nomination outright and force Republicans at their July convention in Cleveland to choose one of them.

Kasich vowed to stay in the race.

"Tonight's results are not going to alter Gov. Kasich's campaign plans," Kasich senior strategist John Weaver said in a campaign memo. "Our strategy has been and continues to be one that involves winning the nomination at an open convention."