Here's a look into the substance and tone of the closed-door meetings:
Trump Listened to Lawmakers' Concerns
Republican House and Senate leaders told ABC News that Trump listened to their concerns and was open to questions and criticisms alike.
"I felt a lot of progress was made. I really do," said House Majority Leader Kevin McCarthy, R-California, who will serve as a Trump delegate at the GOP convention in Cleveland in July.
The meetings overall were described as congenial and straightforward. Sen. John Cornyn, R-Texas, said he enjoyed the opportunity to hear from Trump in a "relatively controlled setting as opposed to in front of 30,000 people."
Cornyn said that Trump's tone was a topic of conversation with Senate leadership.
"Obviously, he’s never run for public office before so this is a new experience for him and for us," he said.
Themes for Trump
The speaker discussed the need for Trump to represent all Republicans, including those who didn’t vote for him, according to a House Republican briefed on the meeting with GOP leadership.
Much of the discussion centered on broad principles that Trump’s campaign can focus on – themes that all Republicans can unify around – as opposed to specific policies, according to several Republican sources. Trump also listened and was receptive to concerns about “respect.”
Trump's Impact on Down-Ballot Races
Trump “recognized the impact of the presidential candidate on down-ballot races and said he looked forward to being helpful where he could,” according to a Senate Republican leader.
The following issues were discussed, according to those in the meetings: Trade, the debt, overreach of agencies, foreign policy, veterans’ issues, abortion, and tax reform. According to one House Republican, Ryan also brought up the need for entitlement reform (his favorite topic, according to many colleagues). “Everybody who knows Paul [Ryan] knows this came up, especially in the contest of balancing the budget,” joked Rep. Charlie Dent, R-Pennsylvania, who spoke with Ryan after the meeting.
House Republican leaders invited Trump to meet with the entire caucus, according to multiple sources. No date has been set, but the expectation is that it will happen before the convention.
The Trump campaign has also begun policy outreach to top Republicans to make sure the campaign and House GOP agenda project -- the election-year platform for Republicans that will be released before the convention -- are in sync, according to Rep. Chris Collins, R-New York, a top Trump supporter in Congress.
Collins said the campaign has begun reaching out to committee chairmen working on the House agenda to solicit policy advice.
Rep. Kevin Brady, R-Texas, chairman of the powerful Ways and Means Committee, said the campaign reached out to his office on Wednesday to trade notes on tax policy.
Some rank-and-file members who have been skeptical of Trump say they still remain wary of endorsing his bid until they see changes in substance and style.
"I've raised a number of concerns. I still have those concerns," said Dent, a GOP moderate who has criticized Trump's comments about Mexican migrants, among other remarks. "Until we see some specific policies and a change in tone, that's what I'd like to see."
Rep. Steve King, R-Iowa, a conservative who backed Sen. Ted Cruz's campaign, said he wants Trump to give a speech on social conservatism.
"There's a large group of conservatives who aren't sold on Trump," he said. "He needs to meet with conservative leaders. He's got to be able to listen."