With the threat of war against nuclear-armed North Korea looming over his administration, President Trump has chosen to engage in a bruising battle with Senate Majority Leader Mitch McConnell that some Republicans fear could have steep consequences as the party turns its attention to tax reform.

A White House official said McConnell enraged Trump earlier this week when he blamed the president's "excessive expectations" for healthcare legislation on his relative newness to Washington, a jab that allies said was unusual for the seasoned political practitioner.

"These are the kinds of things he typically says privately, but is now saying publicly to get the president's attention," a source close to McConnell told the Washington Examiner. "In this instance, he wanted to reassert his view that he knows what's best for getting to 50 votes, and Trump shouldn't interfere on tax reform."

Despite his own attempts to cajole GOP holdouts with private phone calls and White House meetings, Trump made it clear through a series of comments this week that he believes the failure to repeal and replace Obamacare belongs on McConnell's shoulders.

"Can you believe that Mitch McConnell, who has screamed Repeal & Replace for 7 years, couldn't get it done," the president tweeted Thursday, later urging the majority leader to "get back to work" in a separate tweet.

Asked Thursday whether he wants McConnell to cede his leadership position to someone who can deliver on the GOP's agenda, Trump told reporters to follow up on the question if the top Senate Repulblican fails to advance tax, infrastructure and healthcare legislation.

Dismantling the 2010 healthcare law was one of the main agenda items that linked Trump's populist campaign and the rest of the GOP, as he often found himself at odds with other Republicans on issues like trade, immigration and foreign policy during the campaign.

But overhauling Obamacare was a GOP congressional goal long before Trump entered national politics. And the president's allies, like Trump himself, have argued that critics should judge McConnell by the seven-year head start Republicans had to formulate a healthcare plan, not by the seven months in which they failed to pass that plan.

"It boggles my mind that they could have made this such a centerpiece over seven years and not had something ready to go the day after the inauguration," said former Reagan administration staffer Jeffrey Lord, one of the president's favorite on-air surrogates.

Republican Senate aides have expressed optimism that lawmakers will be ready to release their version of a tax reform plan shortly after the White House releases its own, even if the president is still publicly feuding with McConnell — a characterization of events that his own aides have declined to dispute.

"You can see the president's tweets," White House press secretary Sarah Huckabee Sanders told reporters Thursday. "Obviously, there's some frustration."

"The president is distracted by shiny objects, where one week it's [Attorney General Jeff] Sessions he's kicking on, and now, it's McConnell. I don't think this is a sign of chaos to come," said one GOP insider.

A separate source close to McConnell said the Kentucky Republican would never let a series of tweets sink the GOP's chance to restructure the tax code, which he recently described as a "once-in-a-generation opportunity."

"The leader's strategy is to manage expectations and be realistic here because he knows he has a wide range of Republicans with different philosophies on this," the source said.

Some Republicans have suggested the tax legislation could generate even more intra-party dissent than the divisive healthcare battle did, with disagreements lingering over whether cuts should be permanent or expire after a certain number of years. The failure of Obamacare repeal has also denied GOP lawmakers the savings they had hoped to use in their tax calculations.

And many members still disagree over the broad strokes of what the legislation could look like. Some favor a package of tax cuts designed to pass both chambers with relative ease. Others would prefer to see a more comprehensive effort to overhaul tax laws, an approach for which the White House has advocated despite the technical difficulty of uniting enough lawmakers behind such a significant change.

Newt Gingrich, a Trump confidante and former speaker of the House, pushed Republicans on Thursday to avoid setting arbitrary deadlines for the passage of tax reform legislation before congressional leaders know they have the votes to deliver a win.

"I think the initial setting [of] these deadlines, when you don't have a clear plan, when you don't have an absolute majority — there's really not a solid majority in either the House or the Senate," Gingrich told Fox News. "These kind of deadlines create these expectations and then it becomes a crisis, and then somebody has to have failed."

While some remain hopeful that Republicans will come to an agreement on Trump's promised tax overhaul despite escalating tensions between Congress and the White House, other party insiders said they don't have much of a choice.

"We either get something done on tax reform so there's at least one major accomplishment we can tout in 2018, or we get slaughtered next fall," one Senate GOP aide said starkly.