GOP lawmakers fear that President Trump has trampled all over what may have been the best week of his presidency by backing the complete overturn of ObamaCare.

On Monday, the Justice Department asked the U.S. Court of Appeals for the Fifth Circuit in New Orleans to affirm last year's ruling by a Texas federal judge stating that the Affordable Care Act was no longer constitutional because the 2017 tax reform legislation eliminated the health care law’s penalty for not having health insurance.

Multiple congressional Republicans tell Fox News they are bothered by the timing of the Trump administration's intervention in the matter, which comes on the heels of a favorable outcome in the investigation by Special Counsel Robert Mueller, the House sustaining the president's veto of a bill to halt the national emergency for the border wall and a Senate vote that shined a spotlight on problems with the Green New Deal, championed by Rep. Alexandria Ocasio-Cortez, D-N.Y.

"He didn't have to do it now," said House Republican Conference Chair Liz Cheney, R-Wyo., the third-ranking Republican in that chamber.

Still, Cheney emphasized that Republicans want to repeal ObamaCare, and the timing did not bother her.

"We felt vindicated," added one senior House Republican about the end of the Mueller investigation. "We could have ridden this for a few weeks."

"In the South, they put it another way," one senior Democratic lawmaker told Fox News, adding that the president "stepped on his own appendage."

“I’m not going to say the president made a mistake because he said all along he was going to repeal ObamaCare,” said Rep. Bill Johnson, R-Ohio, who represents a sprawling, rural district beset with staggering health care issues and opioid abuse. However, Johnson noted that a bid to repeal and replace ObamaCare failed in 2017, with Republicans in control of both houses of Congress and the White House after years of promising to undo the Affordable Care Act.

“There is merit in the thinking that we missed a golden opportunity,” he said.

Fox News has confirmed that House Minority Leader Kevin McCarthy, R-Calif., spoke to Trump on the phone Wednesday, though McCarthy's office would not characterize the contents of the call. Axios reported earlier Wednesday that McCarthy told the president that the attempt to get the ACA overturned "made no sense."

“ObamaCare is a failure,” McCarthy told Fox News. "The real fear I have is the Democrats’ plan of Medicare for All."

Sources tell Fox News that Republicans are worried they would be blamed if the law is ruled unconstitutional, a decision that would create an immediate vacuum in the American health care system and toss millions of people off health care plans because of pre-existing conditions.

"It will destroy the infrastructure of health care in this country,” said Rep. Donna Shalala, D-Fla., who served for eight years as President Clinton’s Health and Human Services Secretary. "It would be a disaster for 100,000 people in my district."

"Congress isn't going to let 40 million people go without health care," vowed Rep. Mike Johnson, R-La., the chair of the Republican Study Committee, which is trying to prep legislation that would fill the void in the event the law is overturned.

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Cheney described a possible end of ObamaCare as “a situation of desperation on behalf of the Democrats.”

“ObamaCare is unconstitutional,” she said. “We are seeing Democrats push this lie that Republicans don’t want to cover people with pre-existing conditions.”

Fox News' Lukas Mikelionis contributed to this report.