Sen. Pat Toomey, R-Pa., said if Republicans fail to pass either healthcare or tax reform the GOP will likely lose control of the House and probably the Senate.
His comments came during an interview with radio host Hugh Hewitt on Thursday.
"If we don't get either healthcare reform or tax reform done, then I think it's very likely we lose the House and a very reasonable chance that we lose the Senate, too," Toomey said.
"I mean, we've got some reasons why we should pick up seats in the Senate, but hey, people are going to just really, really question whether Republicans can govern. And that's a bad situation to be going into the midterm election with."
Toomey said he is trying to resolve the concerns of Sen. Ron Johnson, R-Wis., about the tax bill.
"Listen, I don't know what Ron is ultimately going to do," Toomey said. "He has concerns that are difficult to completely solve, in my view. He has some valid points. We want to work with him and find a way to get to yes for him."
He insisted Republicans are "very close" to have the votes to push through tax reform.
"This absolutely has to happen," he said. "And you know, I accepted a long time ago that it's not going to be my idea of perfect. That's not going to happen. What it is going to be is much, much better than what we have now, vastly better than what we have now. And that's called progress, and I'm for progress."
The Washington Times reported the House is expected to vote on its tax reform bill on Thursday. The Senate is still completing its tax legislation.