Analysis by Chris Cillizza, CNN Editor-at-large

(CNN) -- When the House Freedom Caucus was formed back in January 2015, here's the mission statement the group released:

"The House Freedom Caucus gives a voice to countless Americans who feel that Washington does not represent them. We support open, accountable and limited government, the Constitution and the rule of law, and policies that promote the liberty, safety, and prosperity of all Americans."

One of the nine founding members of the Freedom Caucus was Michigan Rep. Justin Amash, who had distinguished himself in Congress with his libertarian leanings, unswerving commitment to the Constitution, and efforts to combat the rising US debt. Amash's voting record is regularly one of the most conservative in the House; in 2018, he had a perfect 100% on the Club for Growth vote scorecard, and he has a 99% lifetime score.

In short: Amash is the perfect poster boy for the Freedom Caucus: An unapologetic conservative who is willing to stand up to an establishment GOP which too often compromises rather than fighting on principle.

Which makes Amash's decision to resign from the Freedom Caucus on Monday night all the more telling. "I have the highest regard for them and they're my close friends," Amash told CNN's Haley Byrd of his decision to quit. "I didn't want to be a further distraction for the group."

Amash's resignation from the group he helped form four years ago comes less than a month after the Michigan Republican drew national headlines for a series of tweets in which he said he had concluded -- after reading the Mueller report -- that President Donald Trump had committed impeachable acts.

"Contrary to [Attorney General William] Barr's portrayal, Mueller's report reveals that President Trump engaged in specific actions and a pattern of behavior that meet the threshold for impeachment," Amash tweeted last month.

Those tweets were greeted with condemnation from the House Freedom Caucus, which held an internal vote to condemn their colleague. (Former Freedom Caucus chair Jim Jordan reportedly called Amash soon after his tweets to ask, "What are you doing?") House minority leader Kevin McCarthy was even more blunt, telling Fox News that "it's a question whether [Amash is] even in our Republican conference as a whole," adding: "He never supported the President, and I think he's just looking for attention."

Now, go back to that mission statement for the House Freedom Caucus. You won't find anything in it about unwavering support for a Republican president. Not a single word.

Amash wasn't ostracized by his Freedom Caucus colleagues -- and the broader GOP -- for abandoning the party on principle. (As I noted above, he is one of the most conservative members of Congress year after year.) Instead, he was driven from the Freedom Caucus because he voiced a dissenting opinion about Trump.

And that, in one very simple anecdote, tells you everything you need to now about the current state of the conservative movement and the broader Republican Party in the age of Trump. Being a "conservative" in this day and age means supporting Trump at all time and no matter what. Which is ironic, of course, because Trump wasn't a Republican until a few years before he ran for president in 2016. And even now, he trumpets views -- protectionist on trade, uncaring about debt and deficits, etc. -- that flout what used to be pillars of the modern conservative movement.

Conservatives long prided themselves on the fact that they weren't a movement centered around a person but rather built on a foundation of ideas -- ideas that endured no matter who was in charge or what the political fad of the moment might be. Principles that transcended politics, that embraced the need for hard choices on difficult issues.

Now, for most conservatives in Congress, the movement really amounts to nothing more than a cult of personality. What Trump says goes -- even if it runs directly counter to those once-hallowed principles.

What changed? Well, when the Freedom Caucus initially formed, it was in response to what the members believed to be out-of-control spending and government-building by a Democratic president they loathed. Now, conservatives have a Republican President -- even if he isn't one who, if they are being honest with themselves, has many of the views they claimed to value. Many conservatives have clearly made the calculation that enough of Trump's policies -- deregulation of business, tax cuts, judges -- meet their goals that they will stand behind him no matter what he says or how he behaves. Which is, yes, somewhat short of principled. But is also politics 101.

And, second, well, fear. Trump and his legion of supporters within the party base have shown that any dissenting opinions will be punished. (A state representative announced his plans to primary Amash shortly after the Michigan congressman made his comments.) Self-preservation is a powerful emotion -- and one that seems to have overrun many committed conservatives in the last three years.

The exit of Amash then is rightly understood as further evidence of the total takeover of the conservative movement by Trump. Principle replaced by personality. Foundational beliefs replaced by fear.