-- Lawmakers on both sides of the aisle reacted quickly after White House National Security Adviser Michael Flynn announced his resignation late Monday, calling for more inquiries into Flynn's dealings with Russia.
"Obviously, there's an administration that is in significant disarray, as far as national security is concerned, and they need to fix that," McCain, R-Ariz., said.
Flynn stepped down just days after he apologized to Vice President Mike Pence for misleading him about his conversations with Russia's U.S. ambassador. Flynn came under fire for discussing U.S. sanctions on Russia with the ambassador in December.
House Speaker Paul Ryan told reporters this morning that President Donald Trump "made the right decision to ask for his resignation."
"I think it's really important that as soon as they realized that they were being misled by his national security adviser, they asked for his resignation," Ryan said at a news conference at the Capitol.
The White House so far has said that Flynn offered his resignation. A spokesman for Ryan said it was his understanding that Trump asked for the resignation.
Ryan declined to get into the details of the controversy but said he thinks that "the administration will explain the circumstances that led to this" and that "we need to get all of that information before we prejudge anything."
He did not rule out a special committee to investigate Russia's ties to the administration but noted that "the Intelligence Committee has been looking into this thing all along."
The news prompted a flood of statements from Democrats in Congress, who are pressing for more information.
Reps. John Conyers Jr., D-Mich., and Elijah Cummings, D-Md., issued a joint statement on Tuesday calling for a full classified briefing by "all relevant agencies," including the Department of Justice and the FBI. They said they would submit formal requests this evening.
Rep. Eliot Engel, D-N.Y., the ranking Democratic member of the House Committee on Foreign Affairs, tweeted a statement calling for an investigation into the matter, saying, "Far too many questions remain unanswered about this administration's ties to Russia."
Other Democrats in Congress applauded Flynn's resignation and vowed to press the issue.
Rep. Eric Swalwell, D-Calif., who earlier called for an investigation on Flynn's ties with Russia, said the resignation "isn't the end of the story."
Rep. Adam Schiff, D-Calif., who sits on the House Intelligence Committee, said he wanted to know more about Trump's knowledge of the situation.
House Intelligence Committee Chairman Devin Nunes, R-Calif., was one of just a few Republicans to speak out after Flynn's resignation. Nunes, who has called Flynn a "good friend," thanked him "for his many years of distinguished service."
"Washington, D.C., can be a rough town for honorable people, and Flynn — who has always been a soldier, not a politician — deserves America's gratitude and respect for dedicating so much of his life to strengthening our national security," Nunes said.
ABC News' John Parkinson contributed to this report