Countdown to Their Capitol Hill Meeting: Inside the Donald Trump–Paul Ryan Dynamic

Ahead of the GOP duo's Thursday meeting, a look at their contentious past.

At a rally in South Carolina in February, Trump also blamed Ryan for Romney losing the 2012 presidential election.

Trump and Ryan had a phone call in March to discuss the House Republican's planned election-year agenda. Trump said at the time during a press conference in Washington that Ryan “couldn’t have been nicer.”

Ryan told reporters Tuesday that he and Trump "just need to get to know each other" and work together to find common ground now that the real estate mogul is the GOP's presumptive presidential nominee.

He has repeatedly declined to detail what Trump needs to do to earn his endorsement.

Asked about some of his disagreements with Trump on policy, Ryan said the GOP is a big-tent party with room for disagreement, and focused on the big picture.

"The goal here is to unify the party around common principles,” he said. “We have an obligation to merge and unify around these common principles to offer this country a choice, a better way forward.”

ABC News' Ben Siegel and Mary Bruce contributed to this report.