The meeting took place in the same building at around the same time Republican National Committee Chairman Reince Priebus was briefing rank-and-file House GOP members on the rules for the party's nominating process.
Joe Kasper, chief of staff to California Rep. Duncan Hunter, told CNN he secured the "New York Room," for the sit-down with Manafort, noting the "symbolism" since Trump's home state of New York holds its primary on Tuesday, and the billionaire businessman is favored to win.
Hunter participated, along with the roughly half-dozen members who have endorsed Trump. New York Rep. Chris Collins
, who was the first GOP lawmaker to back Trump, was campaigning in his district and missed the meeting.
The session was the second in what are slated to be weekly meetings with Trump's supporters in Congress. Kasper said there was again discussion Tuesday about the math to get to 1,237 delegates to win the nomination outright, and "there's a high sense of confidence that that number will be exceeded."
Manafort discussed the campaign's reshuffling of staff and the focus on the ground game and delegate process in upcoming contests.
"The campaign has been re-organized to better accentuate the strengths, and includes developing a better ground game in all these states and maintaining a presence in all these states," Kasper told CNN.
Trump's Hill supporters, who are confident he's on a path to getting the nomination, are also urging the campaign to focus more on policy.
Pennsylvania GOP Rep. Lou Barletta said "there were a lot of new faces," including some House Republicans who haven't officially endorsed Trump, who attended the meeting.
He stressed the meeting wasn't about recruiting new Hill backers but the campaign had an "open door policy" to discuss campaign strategy for those who are interested.
Barletta said the campaign is "on full throttle right now" after playing some catch-up to put ground operations in place in upcoming state contests.
"I'm very confident that there is a first class operation in place in Pennsylvania for next Tuesday," Barletta told reporters, noting he participated in two rallies and two office openings in his homestate last week. Pennsylvania's Republicans hold their primary on April 26.