"Anytime you see Club for Growth, it's extortion," Trump said.
Kasich said is has become "extremely difficult" to keep supporting Trump.
Trump campaign events have become increasingly violent in recent days.
The speaker said the entire political system hangs in the balance of this year's elections.
It's a first in the show's more than 20-year history.
His obituary asked friends and family not to vote for the GOP front-runner.
Ann Coulter praised Donald Trump's proposal in a series of tweets.
The candidate posted a series of fake breaking news headlines to poke fun at the media.
"Maybe we should boycott Starbucks," Trump said at a rally.
"You don't have to put on makeup," he said. "Wouldn't it be easier?"