House Speaker Paul D. Ryan (R-Wis.) wants Donald J. Trump to select an conservative with a “proven record” as his vice-presidential nominee, signaling his belief that Trump needs to reassure his party’s right-wing activists that they can trust him.

“I would like someone to assure conservatives that the conservative principles will be adhered to and maintained throughout not just the campaign, but throughout his presidency,” Ryan said Wednesday night in an hour-long town hall with CNN from New York.

As his party’s 2012 vice-presidential nominee, Ryan noted that he is familiar with how this process works and suggested that longtime conservatives still have doubts about the presumptive Republican presidential nominee’s changing views over the last decade on hot-button issues.

“I’d say he’s new to this and he’s been on different sides of different issues, and he has good positions now,” Ryan told CNN’s Jake Tapper. “And on most things, we have common ground.  I just want to make sure that there’s going to be consistency.  I want to make sure that we’re going to have consistent conservatism.”

Ryan has declined to weigh in further about those on the supposed short list of potential running mates for Trump, only to note that Indiana Gov. Mike Pence, who served in Congress with Ryan, was a “personal friend.”

The House speaker, who has been eagerly promoting the new “Better Way” agenda he helped craft in numerous media appearances, reiterated his support for Trump’s candidacy but noted their many clashes on policy issues, such as Trump’s call on a ban from Muslims entering the country and the mass deportation of the roughly 11 million illegal immigrants in the country.

Ryan’s comments on Trump’s vice-presidential selection demonstrated the likely strong resistance Republicans would feel toward retired Lt. Gen. Michael T. Flynn, who is a longtime registered Democrat with conflicting public positions on abortion rights. Trump is said to have Flynn among that short list, which includes Pence, former House Speaker Newt Gingrich and New Jersey Gov. Chris Christie, among others.

Trump has espoused views on key issues that run contrary to Ryan’s own views, particularly on his opposition to trade deals that the speaker helped advance and on overhauling entitlement programs such as Social Security. After Trump knocked out his last opponents in the primary, Ryan used an interview with CNN’s Tapper to question whether Trump was conservative and spent the next month publicly questioning whether he could endorse his party’s nominee.

On Tuesday night, Ryan explained that one of the reasons for endorsing Trump a month later was that it came with the job requirements of being such a prominent party leader.

“I have certain institutional responsibilities as speaker of the House that I think are very important, and it is to help keep our party unified.  It is to respect the will of the primary voter who elected him among the other 16 people running,” he said on CNN, noting that any other move “would have contributed to basically cutting our party in half.”

Many of his own doubts, and those from other conservatives, might be alleviated if Trump chooses a staunch conservative to run with, Ryan said.

“So I think making sure that you have someone that is familiar with and has a proven record of being a conservative reformer who understands conservative founding principles and has experience in applying those principles, that to me, it makes the most difference,” he said.