A day after the GOP presented a united front around the rollout of President Trump Donald John TrumpBubba Wallace to be driver of Michael Jordan, Denny Hamlin NASCAR team Graham: GOP will confirm Trump's Supreme Court nominee before the election Southwest Airlines, unions call for six-month extension of government aid MORE’s tax plan, House Republicans are expressing deep reservations about the Senate’s ability to get the job done.

Lawmakers stung over the failure to pass ObamaCare repeal worry the same fate could befall the tax measure if a handful of senators raise objections.

“Donald Trump won with an electoral landside and his three big campaign points were ObamaCare repeal, tax reform and border security. For a handful of senators to derail that agenda is very frustrating,” said Rep. Blake Farenthold Randolph (Blake) Blake FarentholdThe biggest political upsets of the decade Members spar over sexual harassment training deadline Female Dems see double standard in Klobuchar accusations MORE (R-Texas).

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Rep. Tom Cole (R-Okla.), who is close to the House GOP leadership, says colleagues are frustrated with a handful of senators “overruling the will of the entire House.”

“We do need to see them step up and actually deliver for a change. We have over 200 bills sitting stalled over there. They haven’t been able to deliver on [health care] reform and they all ran on it and now we have a do-or-die moment on tax reform,” he said.

There’s also a sense among House Republicans that their Senate brethren aren't under the same pressure to get results — perhaps because the GOP’s majority in the Senate is seen as safer in the 2018 midterm elections than the House majority.

“They put our majority in jeopardy with their failure on health care, more than they did their own,” Cole said.

While Republicans have a bigger majority in the House than in the Senate, the political map favors the Senate GOP in 2018.

Republicans only have to defend nine seats next year, and only one — held by Sen. Dean Heller Dean Arthur HellerOn The Trail: Democrats plan to hammer Trump on Social Security, Medicare Lobbying World Democrats spend big to put Senate in play MORE (R-Nev.) — is in a state won by 2016 Democratic presidential nominee Hillary Clinton Hillary Diane Rodham ClintonJoe Biden looks to expand election battleground into Trump country Biden leads Trump by 12 points among Catholic voters: poll The Hill's Campaign Report: Biden goes on offense MORE. Democrats are defending more than 20 seats, including 10 in states won by Trump.

In the House, Republicans represent 23 districts carried by Clinton, just shy of what Democrats would need to win to take back the majority.

Republicans are excited about moving to tax reform, and Trump’s plan received enthusiastic support at a half-day private retreat the House GOP held Wednesday to review it.

The president’s proposals to eliminate the estate tax and the alternative minimum tax received ovations.

But the mood turned more somber when Rep. Bruce Poliquin (R-Maine) stood up to ask if the Senate could be counted on to pass tax legislation, according to people familiar with the meeting.

A spokesman for Poliquin did not respond to a request for comment.

“A lot of House members trust a lot of senators to introduce their own tax reform bills,” said Rep. Steve King (R-Iowa), alluding to how senators seek to show independence by offering their own bills.

House Republicans say they can easily see GOP Sens. Susan Collins Susan Margaret CollinsGraham: GOP will confirm Trump's Supreme Court nominee before the election Gardner signals support for taking up Supreme Court nominee this year Tumultuous court battle upends fight for Senate MORE (Maine), John McCain John Sidney McCainBiden's six best bets in 2016 Trump states Replacing Justice Ginsburg could depend on Arizona's next senator The Hill's Morning Report - Sponsored by Facebook - Washington on edge amid SCOTUS vacancy MORE (Ariz.) and Lisa Murkowski Lisa Ann MurkowskiGraham: GOP will confirm Trump's Supreme Court nominee before the election Gardner signals support for taking up Supreme Court nominee this year Tumultuous court battle upends fight for Senate MORE (Alaska), who all voted against a slimmed-down ObamaCare repeal bill in July, bucking the leadership again.

“I do not understand what motivates John McCain,” King said. “I don’t know what goes on in the minds of folks from Maine.”

Earlier this year, in an illustration of the frustration House Republicans hold for the Senate hold-outs, Farenthold joked about challenging Collins to a duel. He later apologized.

McCain later told The Hill that the health-care bill was doomed because it’s virtually impossible to tackle something as huge as reform as health care on a partisan basis.

“If you’re going to pass a major reform, you got to have bipartisan support,” he said.

Speaker Paul Ryan Paul Davis RyanKenosha will be a good bellwether in 2020 At indoor rally, Pence says election runs through Wisconsin Juan Williams: Breaking down the debates MORE (R-Wis.) is making the case that Senate Republicans are more likely to come through on tax reform because McConnell and Senate Finance Committee Chairman Orrin Hatch Orrin Grant HatchBottom line Bottom line Senate GOP divided over whether they'd fill Supreme Court vacancy MORE (R-Utah) have already negotiated a tax reform framework with the administration and House leaders.

“What we did differently in this go around is we spent the last four months basically working together, the Senate Finance Committee, the House Ways and Means Committee and the White House, making sure that we’re on the same page,” Ryan told CNBC’s “Squawk Box” on Thursday morning.

Ryan explained that leaders made sure they did “the hard lifting, the tough work ahead of schedule, ahead of rollout.”

But he also acknowledged that House Republicans have just about run out of patience with the Senate after the collapse of health care reform this week.

“We’re really frustrated. Look, we passed 373 bills here in the House — 270-some are still in the Senate,” he said.

Already there are doubts that Senate Republicans will stick to the plan on taxes.

Hatch, who heads the Senate’s tax writing panel, told reporters Thursday afternoon that he would like to keep in place the deduction for state and local taxes, which the administration wants to eliminate to provide revenue for lower rates.

A spokeswoman for the Finance Committee said, “Chairman Hatch recognizes that every major provision within the tax code has an important constituency and consequence.”