Meanwhile, Trump and his administration seem determined to show that they don’t care about the fortunes of regular people, which isn’t helping.

Nothing is permanent, of course. Trump’s fortunes could revive as all Americans come to realize just how fabulous a president he really is. But if that fails to happen, and his approval ratings remain low, don’t be surprised if he gets a primary challenge for his reelection.

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It has always seemed like the remotest of possibilities, given Trump's apparent hold on his party, and it still may be less than likely. But for this most unusual president, circumstances may combine to bring it about.

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It’s one of the truisms of contemporary presidential politics that a president who gets a primary challenge winds up losing. It’s what happened to George H.W. Bush in 1992 (who was challenged by Pat Buchanan), to Jimmy Carter in 1980 (Ted Kennedy), and to Gerald Ford in 1976 (Ronald Reagan). What’s much less clear is whether the primary challenge is effect or cause: whether it’s that the challenge exposes the president to high-profile criticism and divides his party, or if only weak presidents on the road to defeat get challenged in the first place.

There may be truth in both, but weakness is the necessary condition for a challenge to begin. So what would lead a high-profile Republican, such as former Ohio governor John Kasich or former Arizona senator Jeff Flake (or someone else we haven’t thought of) to challenge Trump?

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The first requirement is that those approval ratings remain low enough that it looks like Trump’s defeat in November 2020 is, if not inevitable, then at least highly likely. At that point even a loyal Republican — candidate or voter — might come to believe that the only thing that would save the party is to have someone else lead the ticket.

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Then there are the things that would keep those approval ratings low, or even drive them lower than they are now. The first is a downturn in the economy, which more and more experts are saying is entirely possible some time in the next two years. While Trump’s claims that he alone is responsible for every good jobs report or up day on the stock market are absurd, like all presidents he gets credit whether he deserves it. Many people say, “Yes, Trump has created a circus, but at least the economy’s doing well.” If that’s no longer true, then what exactly is the rationale for his reelection?

Then, of course, there’s the Russia scandal. At the moment, most Republicans might dismiss it as a witch hunt, but it’s not over — there are more indictments to come, Michael Cohen will eventually testify in public, and who knows what else might be revealed. Even if it doesn’t produce an impeachment, it could still erode Trump’s standing further. That’s not to mention all the other scandals that Democrats in the House will be investigating.

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Nevertheless, even if Trump remains unpopular and Republicans grow more panicky about the possibility of him losing to a Democrat, it will still be a big leap for them to support a challenge, since those challenges have always failed, at least in modern times. But the unusual nature of Trump’s presidency might make the challenge more plausible as something other than a quixotic effort. Yes, a president being defeated for his party’s nomination hasn’t happened since 1884, and only once in U.S. history has a sitting president who won election in his own right lost the nomination (that would be Franklin Pierce in 1852). But we had never elected someone without a day of government or military experience, or someone so manifestly unqualified, or someone who spends his mornings live-tweeting “Fox & Friends.” If all that could happen, why not a successful primary challenge?

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It would take a challenger who sees it as something other than career suicide, and Kasich is the name most often mentioned. He might look to Ronald Reagan’s example as someone who challenged his party’s president, lost and then four years later became president himself.

There is a major difference, however. Like all modern primary challengers, Reagan was coming from his party’s edge and challenging a president he and his followers viewed as not just a failure but as too centrist. That’s what Buchanan and Kennedy argued as well. Nobody is going to outflank Trump on the right; a candidate such as Kasich or Flake would be coming at him from the center. Not that they aren’t extremely conservative, but they wouldn’t be saying Trump isn’t conservative enough.

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That would be a tough argument to make in a primary. Nevertheless, many Republicans believe that Trump’s essential political strategy — always cater to the base’s worst instincts, never reach out beyond your most avid supporters — is fundamentally flawed, particularly for a party that represents a shrinking portion of the electorate. If it looks more and more like the strategy has failed, a challenge could start to seem eminently reasonable.