Rep. Justin Amash, R-Mich., sparked a firestorm of opposition among his fellow Republicans this week when he called publicly for impeaching President Trump. The president responded by calling Amash a “loser,” and the rest of the party apparatus quickly fell in line behind Trump. The head of the Republican National Committee, Ronna McDaniel, criticized Amash for “parroting” the Democrats’ talking points, and conservative commentator Dinesh D’Souza parroted McDaniel by referring to the congressman as the Left’s “useful idiot.” House Minority Leader Kevin McCarthy, R-Calif., denounced Amash for being disloyal to the president and suggested that he may no longer belong in the Republican Party. Even the Club for Growth, one of the Right’s most venerable anti-establishment groups, has criticized Amash for failing to toe the party line on impeachment.

On one level, this is not surprising. The team mentality that characterizes partisan politics has always been a prominent feature of life in the nation's capital. Still, the swift and nearly unanimous outcry that greeted Amash's comments suggests that our party politics has entered a new phase.

This shift is reflected in the fact that Amash's colleagues on the House Freedom Caucus voted this week to condemn his comments. While the Freedom Caucus stopped short of kicking Amash out, a number of its members were nevertheless calling for just that.

Instead of taking formal action to condemn Amash for his policy position on what constitutes an impeachable offense , his fellow Freedom Caucus members could have simply disagreed with him. That a band of former rebels and party outcasts saw that as insufficient is much more revealing of the dysfunction in American politics at present than whether or not the House of Representatives votes to impeach the president.

A group of conservative Republicans formed the Freedom Caucus in 2015 because they were frustrated with being marginalized continuously by their party leaders. They wanted to increase their leverage in intra-party disputes over policy. According to Raúl Labrador , one of the group’s founding members, the caucus was established to give members who were out of step with their colleagues a place to be heard. “That’s the whole purpose of the organization. We have a lot of people here who feel like they are not being heard.”

In response to the Freedom Caucus’ subsequent efforts to push the Republicans to the Right, party leaders removed three conservatives from the whip team and then-Rep. Jason Chaffetz, R-Utah, the chairman of the Oversight and Government Reform Committee, stripped one prominent caucus member of his subcommittee chairmanship. When asked about the retribution, then-Speaker John Boehner, R-Ohio, responded, “I expect our team to act like a team.” An anonymous Republican aide described the sentiment among party officials in less diplomatic terms. “They’re not legislators, they’re just assholes.”

In the past, reactions such as these prompted conservatives to criticize their fellow Republicans for putting party ahead of principle in a naked bid to retain power at any cost. Yet how the Freedom Caucus reacted to Amash’s comments suggests that today even conservatives accept party as the measure of all things. In voting to condemn Amash, members of the Freedom Caucus downplayed the fact that their group was established to prevent its members from being intimidated into remaining silent. In a remarkable turn of events, the Freedom Caucus ostracized one of its own for not toeing the party line four years after the Republican Party tried to ostracize it.

This is a worrisome development because a latent hostility to the freedom of the party's rank and file is inherent in all party bureaucracies. Of course, politics is a team sport. Our two-party system offers most voters a choice between Democratic and Republican candidates in most elections. In that way, party labels help to make politics work, at least in theory, by helping voters to compare and contrast the candidates who are asking for their vote.

But party labels can only do so if there is a party line against which the loyalty of candidates can be measured. And therein lies the problem.

Today, the Republican Party line is ambiguous at best. No one can say precisely what it means to be a Republican because the definition is continually shifting. The only thing of which Republicans appear to be sure is that there is a party line to which they must adhere.

More troubling, the president gets to set the party line at any given moment, not the people’s elected representatives in Congress. Trump captured this well when he called Amash “a total lightweight who opposes me and some of our great Republican ideas and policies just for the sake of getting his name out there.” In the eyes of the party apparatchiks, Amash's apostasy is not that he crossed some clear policy line regarding what constitutes an impeachable offense. Instead, it is that he dared to suggest that Trump, as the very personification of the Republican Party, committed an impeachable offense. In that way, Amash threatened the one thing that defines what it means to be a Republican. He crossed the line.

This explains Republicans’ swift reaction to Amash. The party faithful quickly condemned him instead of letting his constituents decide whether he should be punished because they wanted to affirm their own partisan bona fides. Viewed from this perspective, members of the Freedom Caucus affirmed their loyalty to the Republican Party when they dubbed Amash an apostate merely for expressing support for a policy position with which they disagreed.

Republicans of all stripes would do well to remember the words of one of their party's founding members and leading lights. In 1863, President Abraham Lincoln succinctly captured the essence of what it meant to be a Republican and an American. Back then, the party line was to ensure that “government of the people, by the people, for the people” did not perish from the Earth.

The firestorm sparked by Amash suggests that things have changed.

The new party line to which Republicans appear to give their “last full measure of devotion” is that government of the party, by the party, and for the party shall be protected at all costs.

James Wallner (@jiwallner) is a contributor to the Washington Examiner's Beltway Confidential blog. He is a senior fellow at the R Street Institute. Previously he was a Senate aide and a former group vice president for research at the Heritage Foundation.