President Trump's feud with Sen. Bob Corker, R-Tenn., has Republicans distressed about tax reform, as the raging civil war between the White House and Capitol Hill threatens to sink a major GOP priority and doom their majorities in 2018.

Republicans are relying on a razor-thin, two-vote Senate majority to clear politically complicated tax reform legislation. Trump's public squabbles with Republicans in the Senate contributed to the failure to repeal and replace Obamacare. Alienating Corker, a key vote who has expressed reservations about the direction of his party's emerging tax reform plan, could jeopardize the tax overhaul.

"Tax reform is always very difficult and requires impressive presidential leadership to accomplish. Trump's lack of trust and good relationships on the Hill will make it even harder to accomplish," said Alex Conant, a Republican strategist who advised Sen. Marco Rubio, R-Fla., in 2016 and formerly worked as a congressional aide.

The Republican Party's grassroots and campaign contributor bases are furious about the slow pace of progress under full GOP control of government.

The collapse of legislation to repeal President Barack Obama's Affordable Care Act is a source of tension. Pessimism about tax reform, another crucial promise from the 2016 campaign, has proliferated. And, they don't blame Trump.

The party's most loyal supporters generally hold House and Senate Republicans responsible. If they botch tax reform, their voters, and the financiers of their campaigns, could pull their support and leave the GOP defenseless in the midterm.

To hedge their bets, Republican donors have begun meeting with Steve Bannon, Trump's former chief strategist in the White House who runs Breitbart news, to hear his pitch about funding primary challenges against otherwise safe GOP senators.

"If tax reform doesn't happen, then donors are going to jump ship," said a Republican operative and former congressional leadership aide, who requested anonymity in order to speak candidly.

On Sunday, Trump responded to previous criticism from Corker with one of his signature Twitter tirades. Unusually, Corker responded in kind, and then gave a bombshell interview to the New York Times in which he questioned Trump's fitness for the presidency. Trump resumed their war of words on Tuesday. "The Failing @nytimes set Liddle' Bob Corker up by recording his conversation. Was made to sound a fool, and that's what I am dealing with!" he said on Twitter.

The clash was another front in the ongoing intraparty battle between the president and his presumed allies on Capitol Hill. Both sides are frustrated and blame each other for the stumbles they have experienced since the beginning of the year.

Setting aside arguments about who started the fight and whether Trump's roundhouse attacks on Corker were justified, it remains that the senator holds the keys to the president's legislative agenda, and, as Foreign Relations Committee chairman, key executive branch nominees. Antagonizing Corker might play well in Peoria with Trump's base. Indeed, it might play well with Republicans beyond Trump's base, many of whom are disenchanted with their party's leadership of the Congress.

But it doesn't help along the delicate tax reform process. The president might not care — at least not as much as Republicans in Congress.

"Trump does not count his success by legislative victories. He counts his success by the number of people who show up at rallies and cheer for him," a Republican consultant said. "Unless the Senate gets its act together, the best way for Trump to be successful might be pack rallies and torment the Senate. He views passing legislation as the Senate's problem, not his problem."

Some Republican insiders worry that this is the prevailing White House view, despite all of the effort Trump and his team are putting into the tax negotiations.

Trump told reporters on Tuesday that he's all in on tax reform and won't let his dust-up with Corker get in the way. "People want to see tax cuts, they want to see major reductions in their taxes, and they want to see tax reform — and that's what we're doing. And we'll be adjusting a little bit over the next few weeks to make it even stronger. But I will tell you that it's become very, very popular," he said.

Still, Republicans on the Hill are worried lack of focus from the Oval Office, which dogged healthcare reform, is likely to show itself in the tax talks, although they are largely acknowledged to be running smoother than the Obamacare repeal effort. The key culprits? No trust and no relationships, broadly speaking, between rank-and-file Republicans and the president and his top officials.

"Even Trump's legislative team is antagonistic to the House and Senate," said a GOP operative with clients on Capitol Hill. "Everyone is taking a cue from their leader."