Those specific unpopular political maneuvers coincided with a broader change in the party, from a big tent to more of an exclusive club. No longer was everyone welcome. Changing political labels best exemplified the transformation. In the 1980s, Republicans boasted about Reagan Democrats. In the 1990s, they sneered at RINOs, Republicans in Name Only. It wasn’t just a change in terminology. It was a change in philosophy, from welcoming the heterodox newcomer to kicking out Republicans who didn’t pass their litmus tests on abortion, guns, taxes — you name it.

And here’s the misfire, the point at which the expected functioning of popular democracy failed. The Republican Party had pursued unpopular political maneuvers and purged heretics from its ranks, shrinking the party’s base of support. The result? In 2000, it captured the presidency and retained control over both houses of Congress.

It was a pattern that would repeat itself over the next two decades. Republicans didn’t win every election — in fact, they’ve won the popular vote for president only once in the last 30 years. But they’ve commandeered the government repeatedly despite their unpopularity. Republican policy during the Obama administration made this clear: From debt-ceiling crises to Obamacare repeal to Medicare cuts to government shutdowns to tax cuts for the wealthy, the Republican Party chose the unpopular side of most major policy fights.

This also isn’t just a matter of base politics. Even on issues popular among Republicans, like universal background checks for guns and mandatory gun licensing, Republican politicians hold the line, refusing to budge under the weight of public pressure.

Not every policy that parties pursue is popular. But for the modern Republican Party, almost all of its major policies and political strategies have failed to attain popular support.

That the party has seldom paid a price for that unpopularity points to a troubling feature of modern American democracy: It’s not that democratic. The reasons for that are complex. Some are institutional, like an Electoral College that’s increasingly tilted toward Republican voters and gerrymandered congressional districts that create one-party rule across vast parts of the country. Some are overtly anti-democratic practices, like voter restriction. Some are simply savvy politics, like messaging that disguises the actual policy up for debate, like the infamous labeling of inheritance taxes as “death taxes.”

However one weighs out these various factors, the overall picture remains the same: One of the two major parties no longer feels beholden to public opinion. And that’s why, even though an October Fox News poll indicated that 51 percent of voters favor both impeachment and removal for Mr. Trump, we shouldn’t expect Republicans in Congress to fall in line. Given that not a single House Republican voted yes during the public impeachment inquiry vote that they themselves had requested , we also shouldn’t expect Republicans in Congress to treat the impeachment vote and possible trial with a sense of sober responsibility. We’re no longer in the days of Watergate, where the cumulative weight of public opinion could stir, in addition to a sense of duty, a sense of self-preservation among congressional Republicans. The party has been practicing unpopular politics for decades, and Mr. Trump may well find himself its greatest beneficiary.

Nicole Hemmer (@pastpunditry) is an associate research scholar at Columbia University and the author of “Messengers of the Right: Conservative Media and the Transformation of American Politics.”

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