Presumptive GOP nominee Donald Trump may not have had much support among establishment Republicans during the primary, but a panel of three GOP members of Congress said Sunday that they're backing Trump and are confident he'll do what needs to be done to unify the party.

Rep. Chris Collins (R-N.Y.), one of Trump's first congressional endorsers, said he's backing the candidate because of his executive experience.

"The reason I threw my weight behind and my support behind Donald Trump is ... he was the only chief executive," Collins said. "And I feel like that's a very important attribute with everything this nation is facing."

And despite claims that Trump has been changing his stance on some issues--his Muslim immigration ban among them--Collins said Trump is just now starting to dig into substantive policy issues.

"You're just now seeing Donald Trump the nominee moving into the policy area," he said. "So as he ran for the nomination, that's not to say that he did anything other than the 30,000-foot level."

Rep. Marsha Blackburn (R-Tenn.) said she's encouraged by Trump's outreach on Capitol Hill, saying he has "listened to the American people."

"I quite frankly am encouraged he's trying to find common ground" with congressional Republicans, she said. "I think that's a wonderful opportunity for us, and it's an opportunity for the American people. You're probably going to see a very aggressive legislative agenda. I look forward to a first 100 days of the President Trump administration."

She added that she's confident House Speaker Paul Ryan will come to support Trump in the near future.

"I think you're going to see Paul Ryan move very quickly toward working with Donald Trump and unifying the Republican Party," she said. "And quite frankly, I think we're going to have the most dynamic campaign this fall that we have had in decades."

Even New York Rep. Peter King, who said he has some "real questions" for Trump on national security, said he'll be voting for and supporting Trump this fall.

"There's a lot about Donald Trump I like, he's brought people into the Republican Party, he's brought in the blue-collar Reagan Democrats," King said.

Still, he added: "Before I can actively campaign, I have to see a much more coherent foreign policy."