House Speaker Paul Ryan joined in singling out some of the most conservative members of his party Thursday, saying that he understands the frustration aimed at them after their role in last week's failure of a GOP health care bill. Ryan's comments echoed the warning sent by President Donald Trump on Twitter earlier in the day, putting more pressure on the key bloc of Republican House members known as the Freedom Caucus.

“It is very understandable that the president is frustrated that we haven’t gotten to where we need to go because this is something we all said we would do,” Ryan said when asked about Trump's tweet. “So he is just expressing his frustration. ... And I understand his frustration.”

Trump's tweet targeted those conservatives, saying they “will hurt the entire Republican agenda if they don’t get on the team,” and threatening to "fight" them in the 2018 midterm elections. Those comments escalated an intra-party feud that peaked last week when Republicans were unable to find enough Republican votes to pass their health care bill.

Related: Trump Spurns Bipartisanship, Vows to ‘Fight’ Fellow Republicans in 2018

And members of the Freedom Caucus were quick to return the fire, defending themselves and their principles.

“It's constructive in fifth grade," Rep. Justin Amash, R-Mich., a member of the group, said of the tweet. "It may allow a child to get his way but that's not how our government works.”

Another caucus member, Rep. Jim Jordan, said their demands are helpful to the president.

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"We’re trying to help the President, but the fact is you got to look at the legislation and it doesn’t do what we told the voters we were going to do," Jordan said on Fox News. "And the American people understand that. That’s why only 17 percent of the population supports this legislation."

The House Freedom Caucus, a group of about 35 conservative lawmakers who believe in very little government, have been a constant thorn in the side of Republican leadership in recent years. Many of them were elected in the tea party electoral waves of 2010 and 2012 and have pushed the Republican Party to the right on a range of issues.

The group, which has enough members in its bloc to prevent a bill from passing on a strict party-line vote, are reluctant to support any legislation or funding bill that doesn’t reduce the government’s footprint. They have helped force government shutdowns over funding bills and were instrumental in former House Speaker John Boehner’s struggles that led him to abruptly resign.

Now they are a problem for the agenda that Trump and Ryan are seeking to enact.

"You can't allow 30 to 35 people to hold the whole Republican conference hostage," said Rep. Peter King, R-N.Y. and ally of Ryan. "They're playing tough, he's playing tougher."

Even though some moderates also opposed last week's bill, most of the frustration is aimed at conservatives who balked at accepting a compromise and the tensions have spilled into the public after they were unable to pass their signature legislation — a total repeal of the Affordable Care Act, also known as Obamacare.

Moderate Republicans, who are members of a subgroup of Republicans called the Tuesday Group, agreed at a meeting Wednesday night to not negotiate with the conservatives on health care, according to a source. That's a move that not only hampers prospects for a revived push in legislation, but could further alienate the conservatives.

"We’d rather work with our leadership," said Rep. Tom MacArthur, a co-chair of the Tuesday Group. "Our concern is it's not healthy for small groups of people outside the real process to be cutting side deals so we wanna work with all of our members."

The Freedom Caucus, however, has many similarities to Trump. Most members ran on an anti-establishment platform, critical of Washington and Republican leadership, similar to Trump’s.

So Trump’s criticism of the Freedom Caucus makes no sense, said Rep. Dave Brat, R-Virginia, who beat former House Majority Leader Eric Cantor in a primary in 2014.

“(Trump) ran on the exact same things that we all ran on. Drain the swamp. Repeal Obamacare,” Brat said, adding that he thinks Trump is receiving bad advice. “We all ran with the president. The never-Trumpers weren’t with trump. We’re clean the swamp guys, we’re the ‘let’s listen to the American people guys, so he knows that.”

If Trump does try to target this conservative group in 2018, he has an additional challenge: Almost all of the staunchly far-right members he would be targeting have enjoyed comfortable re-election margins in some of the country’s most conservative districts.

And they have bases of support that could prove to be more resilient than Trump’s in their home district.

In fact, of more than 30 members of the House Freedom Caucus, all but three outperformed Trump in their own district in 2016, winning a greater share of the vote than the top of the GOP ticket.