Republican National Committee chairman Reince Priebus is “furious” with Donald Trump and senior GOP officials are “actively exploring” about how to replace Trump on the ticket if he were to drop out, ABC News reports Wednesday.

Priebus has had multiple discussions with Trump in the past few days telling him that he needs to get back on message. On Tuesday, Trump refused to endorse Speaker of the House Paul Ryan and Arizona Sen. John McCain in their respective primaries.

“I am told that senior officials at the party are actively exploring what would happen if Trump dropped out. How to replace him on the ballot,” ABC’s Jon Karl said on Good Morning America. “They can’t force him out, he would have to go out voluntarily. And then it would be the 168 members of the RNC through a complicated process they would pick a new candidate.”

“They are so unable to control his message, they just don’t know, they clearly think it is a possibility,” Karl added.