A top Republican National Committee official believes Sen. Ted Cruz Rafael (Ted) Edward CruzMurkowski: Supreme Court nominee should not be taken up before election Battle lines drawn on precedent in Supreme Court fight Sunday shows - Ruth Bader Ginsburg's death dominates MORE (R-Texas) would run for president in 2020 even if Donald Trump Donald John TrumpBiden leads Trump by 36 points nationally among Latinos: poll Trump dismisses climate change role in fires, says Newsom needs to manage forest better Jimmy Kimmel hits Trump for rallies while hosting Emmy Awards MORE is the sitting president.

“If Trump wins, you better bet your ass Cruz is going to primary him,” an unnamed RNC official told Yahoo News.

ADVERTISEMENT

Cruz faced off with Trump in a bitter GOP presidential primary this year, eventually ending his campaign after losing the Indiana primary in May.

The Texas senator has not yet endorsed Trump but has accepted a speaking slot for the Republican National Convention's Wednesday night session.

Hours before Cruz was scheduled to speak, he held a thank-you event for his delegates and supporters in Cleveland. At the event, any mention of Trump drew loud boos from his supporters.

Attendees also chanted "2020" during the event.

"I don't know what the future is going to hold, I don't know what will happen, but what I do know is my unshakable faith in the men and women here," Cruz told his supporters.