Trump vows to ‘fight’ Freedom Caucus in 2018 midterms. Caucus members fire back. | McClatchy Washington Bureau

President Donald Trump effectively declared war Thursday on the House Freedom Caucus, the powerful group of hard-line conservative Republicans who blocked the health-care bill, vowing to "fight them" in the 2018 midterm elections.

In a morning tweet, Trump warned that the Freedom Caucus would “hurt the entire Republican agenda if they don't get on the team, & fast.” He grouped its members, all of them Republican, with Democrats in calling for their political defeat — an extraordinary incitement of intraparty combat from a sitting president.

There are about three dozen members of the Freedom Caucus, and most of them were elected or reelected comfortably in solidly Republican districts. With his tweet, Trump seemed to be encouraging primary challenges to each of them in next year's elections.

[Trump blames House Freeom Caucus for failure of health care bill]

[This Freedom Caucus member tried to strike a health care deal – with waffles]

House Speaker Paul Ryan, R-Wis., told reporters late Thursday morning that he sympathized with Trump.

"I understand the president's frustration," said Ryan, who has unable to push the health-care bill through his own chamber. "I share frustration. About 90 percent of our conference is for this bill to repeal and replace Obamacare and about 10 percent are not. And that's not enough to pass a bill."

Ryan said he had no immediate plans to bring the health-care bill back to the House floor.

"This is too big of an issue to not get right, and so I'm not going to put some kind of artificial deadline on saving the American health-care system from oncoming collapse," said Ryan, who initially scheduled the bill's passage for the seventh anniversary of the Affordable Care Act's signing.

Trump and his White House advisers have been frustrated by the intransigence of Freedom Caucus members, led by Rep. Mark Meadows, R-N.C. Trump lobbied them intensively to support the GOP plan to replace President Barack Obama's signature Affordable Care Act, only to see the bill collapse last Friday after Meadows and some of his allies said they would not vote for it.

"This has been brewing for a while," a White House official said of Trump's decision to target Freedom Caucus members and other GOP foes.

Trump has been "paying close attention and keeping his options open," said the official, who was not authorized to speak publicly and requested anonymity to do so. "Our view is: There's nothing as clarifying as the smell of Air Force One jet fuel. So if he needs to bring in the plane and do a rally, he's going to think about doing that."

The official added that Trump and White House aides are "sick and tired" of seeing Freedom Caucus members on television in recent days.

Trump's threat comes as Republican leaders are bracing for a month of potential GOP infighting over spending priorities. Congress must pass a spending bill by April 28 to avert a government shutdown, but the path ahead, as in recent spending battles on Capitol Hill, is narrow and filled with obstacles.

Beyond that, the same divide that derailed the health-care legislation could imperil the next marquee legislation Trump wants to tackle: tax reform.

White House press secretary Sean Spicer told reporters Thursday that Trump remains committed to "a bold and robust agenda," adding: "He's going to get the votes from wherever he can."

Spicer said it would be improper for him to comment from the White House briefing room about Trump's electoral plans.

Most Freedom Caucus members were elected from very safe Republican districts, and many of them faced no primary opposition in their last election. To make good on his threat, Trump would have to recruit GOP candidates to make the case that the Republican incumbent they face was unhelpful to the president.

Though Trump's job approval numbers are sagging, he remains quite popular in many of the districts from which the Freedom Caucus members were elected.

"He's irritated," anti-tax advocate Grover Norquist said in explaining Trump's decision to lash out at Freedom Caucus members. "During the health-care discussions, the Freedom Caucus would say they'd support him if they got one thing, then they'd want another thing. If you're Trump, you wonder, 'Why are these people meeting with me if they're always going to be a no vote?' There was room for give and they wouldn't give."

If Trump gets involved in Repbulican primaries, Norquist said he thinks it's possible Trump could "get some scalps."

On Capitol Hill, Trump's tweet was met with a range of reactions - with some members saying it could prove counterproductive and others praising him for using the power of his office in a way he hasn't to this point.

Rep. Mark Sanford, R-S.C., a former governor who has called for the health reform to work its way through Congress more slowly, said that the president was taking exactly the wrong approach to his fellow House Freedom Caucus members.

"The idea of threatening your way to legislative success may not be the wisest of strategies," Sanford said Thursday. "His message yesterday was that he wanted to work with Democrats; I guess the message today is 'we need to fight against Freedom Caucus members and Democrats.' That's a conflicted message. It's a case of shooting messengers who were, rightfully, pointing out problems in a bill that the American public has not shown a proclivity toward."

Rep. Jim Jordan, R-Ohio, a Freedom Caucus member, said the break with Trump on the health-care legislation was based on real policy differences, not a lack of loyalty.

"The president can say what he wants and that's fine. But we're focused on the legislation," Jordan told reporters.

Some of the harshest responses to Trump came via Twitter, his preferred means of provocative communication.

Those included a tweet from Rep. Justin Amash, R-Mich., who said that Trump's support of the health-care bill signaled he was now part of the Washington establishment that he had campaigned against.

"It didn't take long for the swamp to drain @realDonaldTrump," tweeted Amash, a member of the Freedom Caucus and one of Trump's frequent GOP critics. "No shame, Mr. President. Almost everyone succumbs to the D.C. Establishment.”

Rep. Kevin Cramer, R-N.D., who's not part of the Freedom Caucus, said he was among the members sympathetic to Trump, however.

"There's a fair number of us who are applauding him," said Cramer, adding that he saw the tweet as being true to Trump's blustery, aggressive nature. But Cramer, an early Trump supporter, also acknowledged some members would only be emboldened by the tweet.

Rep. Chris Collins, R-N.Y., said Trump's focus on the Freedom Caucus is well-placed.

"He's obviously frustrated, as many of us are, and there's only one place where the finger-pointing should go, and that's to the Freedom Caucus," he said.

And Collins, a member of the moderate Tuesday Group, rejected any notion - put forth this week by members of both groups - that there could be an accommodation on the health-care bill forged between them.

"The Tuesday Group will never meet with the Freedom Caucus, with a capital N-E-V-E-R," Collins said.

The only way the health-care bill could be rekindled, he added, would be if Freedom Caucus members became willing to accept a bill that was substantially the same as the one that failed Friday.

"Frankly, I don't see that happening," he said.

Sen. Rand Paul, R-Ky., an ally of the House Freedom Caucus, said that "lines of communication are still open" between caucus members and the White House. Asked to respond to Trump's threat, Paul said he thought the White House could reach a compromise and stopped short of criticizing Trump's tactics.

Asked about Trump's tweet targeting the Freedom Caucus, Sen. John McCain, R-Ariz., said on Thursday: "I really do think they need to get on board, but I'm not sure that that's the proper approach to them because they are elected by their constituents."

Michael Steel, who was a senior aide to then-Speaker John Boehner, R-Ohio, said there is potential in some districts for Trump to dislodge Freedom Caucus members if he puts his political organization behind the effort.

"If the president chooses to support primary challengers to House members who've been unhelpful, it wouldn't necessarily be an ideological challenge," Steel said. "It would be based on loyalty to the president, or lack thereof."

But Steel added: "You don't necessarily have to wait for 2018 for this to have an effect. Even the threat could work in the short term."

There is precedent for Republican leaders taking aim at Freedom Caucus members. A spate of 2015 ads purchased by the American Action Network, a nonprofit issue advocacy group with ties to House GOP leaders, targeted Jordan and two other hard-liners for opposing a Department of Homeland Security funding bill.

Those ads infuriated members of the Freedom Caucus, then only months old, and launched a confrontational relationship that culminated in Boehner's resignation six months later.

One open question is whether the National Republican Congressional Committee (NRCC), the GOP's House campaign arm, would intervene on behalf on incumbents in the Freedom Caucus. The committee recently changed its policy to allow spending to protect incumbents in certain GOP primaries.

Rep. Steve Stivers, R-Ohio, the NRCC's chairman, chuckled Thursday after a reporter read him Trump's tweet about the Freedom Caucus and asked him whether the NRCC might intervene in primaries on behalf of the group's members.

"I want to be very clear: We have a policy of helping out incumbents that pay their dues," Stivers said, referring to the hundreds of thousands of dollars GOP lawmakers are expected to raise for the committee each election cycle. "As long as If they pay their dues, we're gonna be there for them. ... If I was them, I'd take a look and see how I'm doing on my dues."

Republicans, meanwhile, were at odds Thursday about the wisdom of working with Democrats on health care.

In a television interview that aired Thursday morning, Ryan said that he does not want Trump to work with Democrats on new legislation for revamping the Affordable Care Act.

"I don't want that to happen," Ryan said on "CBS This Morning."

Those comments were criticized by Sen. Bob Corker, R-Tenn., who said: "It's not the kind of thing that the leader, the speaker of a House, should be saying."

Corker said that he has a "lot of respect" for both Ryan and members of the House Freedom Caucus. But he said he sees "zero overlap" in health-care policy plans between Trump and the Freedom Caucus.

"I see an impossibility of President Trump putting forth a piece of legislation on health care that he supports and the Freedom Caucus supports," Corker said. "Unless -- unless one of the two is willing to give up their principles."