After President Trump threatened war against the House Freedom Caucus for 2018 in a Thursday morning tweet, members of the caucus were quick to respond.

Michigan Rep. Justin Amash took aim at Mr. Trump’s oft-repeated desire to “drain the swamp” in Washington, a phrase meant to evoke Washington lobbying, big money in politics, and corruption.

It didn't take long for the swamp to drain @realDonaldTrump. No shame, Mr. President. Almost everyone succumbs to the D.C. Establishment. https://t.co/9bDo8yzH7I — Justin Amash (@justinamash) March 30, 2017

The Freedom Caucus has borne the brunt of the blame for the embarrassing failure of the Republican-sponsored health care bill last week, though several moderates also opposed the bill. The White House has indicated it could make some overtures toward Democrats for help on health care, but House Speaker Paul Ryan opposes this.

Get Breaking News Delivered to Your Inbox

“If this Republican Congress allows the perfect to be the enemy of the good, I worry we’ll push the president into working with Dems,” Ryan said, in an interview with CBS News’ Norah O’Donnell on “CBS This Morning.”

Rep. Thomas Massie, R-Ky., like Amash, also mentioned the “swamp,” linking it to the House Republicans’ health care bill. Massie is aligned with the Freedom Caucus, but not officially a member of the group.

.@realDonaldTrump it's a swamp not a hot tub. We both came here to drain it. #SwampCare polls 17%. Sad! https://t.co/4kjygV2tdS — Thomas Massie (@RepThomasMassie) March 30, 2017

The main concerns espoused by the former chairman of the Freedom Caucus were in the GOP health care measure itself, and not the president’s comments.

The bill, he said, “doesn’t fully repeal Obamacare. This bill doesn’t lower premiums, and probably most importantly, this bill doesn’t unite Republicans and the American people,” Ohio Rep. Jim Jordan told Fox News’ “America’s Newsroom.”

”[W]e appreciate the president, we’re trying to help the president, but the fact is you’ve got to look at the legislation,” Jordan continued. “And it doesn’t do what we told the voters we were going to do, and the American people understand that.”

Here’s Mr. Trump’s original tweet, posted Thursday morning:

The Freedom Caucus will hurt the entire Republican agenda if they don't get on the team, & fast. We must fight them, & Dems, in 2018! — Donald J. Trump (@realDonaldTrump) March 30, 2017

The statement marked the first time Mr. Trump has openly opposed the political future of the Freedom Caucus in Congress.

What is the Freedom Caucus?

The group, which now numbers at least 30 of the most conservative members in the House of Representatives, was founded by Jim Jordan in 2015. They stand for minimal regulation, lower taxes and smaller government. The group played a pivotal role in the failure last week of the House Republican plan to replace the Affordable Care Act. The caucus’ opposition, along with that of some moderates, meant the bill lacked the support to pass the House.

Before that, the caucus members helped to force former Speaker John Boehner out as speaker, largely because they felt he capitulated too frequently to Democrats. After he stepped down, Freedom Caucus members circulated a questionnaire revealing what they wanted to see in a new speaker, including a question that was a litmus test for the new speaker: “Would you ensure that the House-passed appropriations bills do not contain funding for Planned Parenthood, unconstitutional amnesty, the Iran deal and ObamaCare?”