The Senate’s second-ranking Republican joined other GOP lawmakers on Tuesday calling for an investigation into President Donald Trump’s ties to Russia. The outcry comes after the resignation of national security adviser Michael Flynn late Monday over his conduct during and after phone calls last year with the Russian ambassador to the U.S.

John Cornyn, the Senate Majority Whip and a member of the Senate Intelligence Committee, told reporters that the House and Senate intelligence committees should conduct an investigation. Asked by the Dallas Morning News whether Flynn should testify, Cornyn said, “That would certainly be an option.”

Flynn’s resignation came after reports that he’d misled Vice President Mike Pence and other Trump administration officials about the nature of his conversations with Russian ambassador Sergey Kislyak — specifically, whether they discussed sanctions imposed by the Obama administration in response to intelligence community reports that Russia attempted to influence the U.S. presidential election.

While Pence, White House Press Secretary Sean Spicer, and others insisted in public statements that Flynn hadn’t discussed sanctions during those texts and phone calls, multiple reports indicated U.S. intelligence officials had evidence that sanctions did come up. Flynn acknowledged in his resignation letter that he “inadvertently” provided “incomplete information” about his communications.

On Tuesday, Spicer confirmed in a press briefing that Trump had been told more than two weeks before that Flynn had not told the truth about what was discussed during the calls. Spicer said Trump and others in the administration had been “reviewing and evaluating this issue on a daily basis trying to ascertain the truth.”

While Republican leaders had been reluctant to press Trump on his friendliness toward Russia, Flynn’s resignation appeared to make several in the Senate far more eager to launch an investigation.

Missouri Sen. Roy Blunt, another Republican member of the Senate Intelligence Committee, told Missouri radio station KTRS that “everybody needs that investigation [into Flynn’s conduct] to happen,” and that Flynn should speak to lawmakers “very soon.” Blunt, however, stopped short of calling for Flynn to testify publicly.

“The Senate Intelligence Committee, again that I serve on, has been given the principal responsibility to look into this,” Blunt said, “and I think that we should look into it exhaustively so that at the end of this process, nobody wonders whether there was a stone left unturned, and shouldn’t reach conclusions before you have the information that you need to have to make those conclusions.”

Russia hawks in the Senate called on Flynn’s conduct to be part of an ongoing Senate Intelligence Committee investigation into Trump’s ties to Russia. South Carolina Sen. Lindsey Graham said Congress needs more information on what exactly Flynn told the ambassador.

“I want to know, did Gen. Flynn do this by himself or was he directed by somebody to do it?” Graham said on CNN.

GOP Sen. John McCain of Arizona said in a statement that Flynn’s “resignation is a troubling indication of the dysfunction of the current national security apparatus,” adding that it “raises further questions about the Trump administration’s intentions toward Vladimir Putin’s Russia.”

Most House Republicans, meanwhile, were either reluctant to press the issue or altogether silent.

Rep. Jason Chaffetz, the chairman of the House Committee on Oversight and Government Reform, said his committee won’t investigate Flynn. Rep. Devin Nunes, chairman of the House Intelligence Committee, reportedly said he wouldn’t investigate Trump’s conversations with Flynn. He added that leaks to the press were the real concern.

House Speaker Paul Ryan declined to commit to an investigation into Flynn’s conduct.