(CBS) - Senator Lindsey Graham, R-South Carolina, said Sunday that if the GOP doesn't act on tax reform, just one item on Congress' agenda, "we're dead."
"If we don't cut taxes and we don't eventually repeal and replace Obamacare, then we're going to lose across the board in the House in 2018," Graham said. "And all of my colleagues running in primaries in 2018 will probably get beat."
"It will be the end of Mitch McConnell as we know it," he added. "So this is a symptom of a greater problem. If we do cut taxes and we do repeal and replace Obamacare, it doesn't matter what Bannon [will] do because we'll win."
Graham's comments follow a Vanity Fair article that said former Trump adviser Steve Bannon told people -- according to a source -- he believes Mr. Trump only has a 30 percent chance of finishing his first term.
Bannon has since refuted the claim, predicting at a Voters Summit on Saturday that his former boss will not only finish out his first term, but win a second term with 400 electoral votes in 2020.
"He's a symptom of a problem. Bannon can't beat us if we're successful. And if we're not successful, it doesn't matter who tries to beat us, they'll be successful," said Graham.
But Graham reiterated his concerns about Congress' busy agenda, saying, "We promised to cut taxes and we have yet to do it. If we're successful, Mitch McConnell's fine. If we're not, we're all in trouble."
The senator also suggested that if Congress doesn't follow through, "We lose our majority and I think President Trump will not get reelected."
Graham's remarks came after Mr. Trump announced on Thursday his latest effort in "demolishing" Obamacare, signaling that the federal government would be ending key cost-sharing subsidies under the Affordable Care Act.
The cost-sharing reduction payments, paid to insurers, were a component of Obamacare that made health insurance more affordable for qualified individuals and families. Ending the subsidy payments poses a major threat to the ACA -- it's likely to cause premiums to skyrocket for patients who purchase insurance on the exchanges.
Graham said that Mr. Trump has now urged lawmakers to find a bipartisan solution to continue those payments, but it would have to be a "good deal" to get Mr. Trump's support.
"The president is not going to continue to throw good money after bad, give $7 billion to insurance companies unless something changes about Obamacare that would justify it," said Graham, who has recently spent time golfing with the president.
Meanwhile, Graham said that Mr. Trump is also pushing Congress to get a better nuclear deal with Iran, something he called a "miserable failure."
"The president ran on the idea this is a bad deal for America and he won. He's fulfilling a campaign promise. This is a terrible deal for America and the region," Graham said of the Iran nuclear agreement.
The senator said he was encouraged by suggestions for a fix posed by his colleagues, Sens. Bob Corker of Tennessee and Tom Cotton of Arkansas.
"Congress is going to say to the Iranians that if you ever try to get within a breakout time less than a year, we're going to reimpose sanctions. We're going to look at your missile program anew. We're going to make sure that we inspect any place. And if you don't allow us to inspect, we're going to re-impose sanctions. And if you're still sponsoring terrorism, down the road we're going to re-impose sanctions," said Graham.
Graham said, of his colleague Corker, that it "breaks his heart" he is leaving the Senate after 2018, amid brewing tensions with the president.
"He's [Corker] one of the most valuable members of the Republican Conference. He and the president have gotten into this Twitter war. At the end of the day, I played golf with the president yesterday. He is not a man under siege. He beat me again, like a drum. We had a good time."
He suggested that Mr. Trump, however, is "hell bent on getting a better deal."
"He promised to tear it up and he's decided not to tear it up. He's decided to decertify, which I think he's right to do, and push the world and Congress to get a better deal before it's too late, said Graham."
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