Updated 10 a.m. ET
Escalating tension between Capitol Hill and the White House is threatening the GOP's legislative agenda and testing the bonds of party unity under the Trump administration.
An unscripted and angry President Trump unloaded on Congress at a campaign rally in Phoenix, leaving lawmakers increasingly apprehensive about the party's ambitious fall agenda that includes an overhaul of the entire federal tax code.
Instead of hammering that message, the president used his bully pulpit to criticize Republicans for failing to pass a long-promised health care bill to dismantle the Affordable Care Act.
"Obamacare is a disaster and think — think! We were just one vote away from victory after seven years of everybody proclaiming 'repeal and replace!' One vote away!" Trump said, in reference to Sen. John McCain, R-Ariz., who cast the decisive vote in the Senate.
Trump did not name McCain, who is undergoing treatment for brain cancer, but his intention was clear.
"It's disappointing is probably the most nice thing I can say about that," Rep. Adam Kinzinger, R-Ill., told CNN in response to Trump's comments about McCain.
Trump also implicitly attacked Arizona's junior senator, Jeff Flake, who has been one of the party's most vocal Trump critics. The president said Flake is "weak on borders and weak on crime" and that "nobody knows who the hell he is."
The president called on the Senate to end the chamber's defining characteristic — the filibuster — in order to lower the threshold for most legislation from 60 votes to 51 and force his agenda through Congress. There is bipartisan opposition to doing so in the Senate. The health care bill failed in July despite being produced under a process that required only 51 votes.
Trump even threatened a government shutdown in September if Republicans don't deliver him a spending bill that includes the money he wants to start building a wall on the U.S.-Mexico border.
"Now the obstructionist Democrats would like us not to do it, but believe me, if we have to close down the government, we're building that wall," Trump said, to a cheering crowd in Arizona, just hours after visiting a U.S. Customs and Border Patrol facility. Speaking to reporters on Air Force One on Wednesday, White House press secretary Sarah Huckabee Sanders said that Trump "has definite plans to make sure that it gets built," but would not reiterate the shutdown threat.
At a Wednesday event in Oregon to promote upcoming tax legislation, House Speaker Paul Ryan was instead forced to answer questions over whether Republicans are going to shut down the government. "I don't think anyone is interested in having a shutdown. I don't think it is in our interests to do so," Ryan told reporters.
Senate Majority Leader Mitch McConnell tried to tamp down on reports that he and the president are at odds and have not spoken in weeks.
In a statement on Wednesday, McConnell said he is in "regular contact" with Trump about their "shared goals" that include tax, infrastructure and defense bills, as well as plans to fund the government and raise the debt ceiling, the nation's legal borrowing limit needed to pay the nation's bills.
"We have a lot of work ahead of us, and we are committed to advancing our shared agenda together and anyone who suggests otherwise is clearly not part of the conversation," McConnell said.
The White House responded with a similar statement, saying the two men "remain united on many shared priorities." Still, Trump sent tweets critical of McConnell and Ryan on Thursday morning.
Sanders was asked about the New York Times report of McConnell expressing doubt that Trump can salvage his presidency, and whether being so tough on Senate Republicans is the right approach. She told reporters traveling with Trump on Wednesday, "I think everybody knows this president isn't somebody who backs down, and if he thinks that you need to lean in a little bit, he certainly will."
But what's also clear is that if Trump continues to provoke Republicans — like he has by suggesting he could support an opponent to Flake in his Senate GOP primary — that will put him firmly at odds with McConnell. The Senate GOP campaign operation as a matter of policy supports all of its incumbents for re-election, and Flake is widely seen as the best candidate to keep Arizona a GOP-held seat. This week, the Senate Leadership Fund, a superPAC close to McConnell, ran a digital attack ad against a GOP candidate opposing Flake whom Trump has voiced support for.
It's also clear that frustrations are rising over the August break because of the president's ambiguous response to the racist violence in Charlottesville, Va., as well as his continued inability to focus his message to promote the GOP plan to overhaul the tax code.
Democratic opposition, meanwhile, has deepened, and as a result lowered the already dim prospects for bipartisanship.
A group of House Democrats has introduced a censure resolution — or formal rebuke — of the president for his handling of Charlottesville. At least 78 Democrats have signed on as co-sponsors. Also in August, Rep. Steve Cohen of Tennessee became the third Democrat to formally call for moving forward with articles of impeachment against Trump.
House Minority Leader Nancy Pelosi and Senate Minority Leader Chuck Schumer have already said they oppose GOP efforts to include money in a pending spending bill to pay for a border wall. Pelosi reiterated that opposition Wednesday.
"President Trump's multibillion-dollar border wall boondoggle is strongly opposed by Democrats and many Republicans. Democrats will stand fast against the immoral, ineffective border wall," she said in a statement.
Congress returns Sept. 5, and there are only 12 legislative days that month to find at least short-term solutions to keeping the government open and raising the debt limit.
Republicans are increasingly candid about their apprehension about what is to come this fall.
"[The president's] hands, at the end of the day, are going to be driven by what the Legislature does or does not do, and you better find a way to work with them because at the end of the day they can, again, stymie your efforts or they can actually move them forward," Rep. Mark Sanford, R-S.C., a former governor, told CNN. "And so it's a real problem from the standpoint of him advancing his legislative agenda."