Just about every election cycle, there’s an argument for why, this time, things might be different — different from expectations based on historical trends and key factors like the state of the economy or the president’s approval rating.

The arguments are often pretty plausible. After all, every cycle is different. There’s almost always something unprecedented about a given election year — in just the last few cycles, the pandemic, the first female presidential major party nominee and the first Black president were all truly novel. There’s always a way to spin up a rationale for why old rules won’t apply.

In the end, history usually prevails. That’s a good thing to keep in mind right now as Democrats show strength that seems entirely at odds with the long history of the struggles of the president’s party in midterm elections.

But this cycle, there really is something different — or at the very least, there is something different about the reasons “this cycle might be different.”

This cycle, the arguments for Democratic strength cut at the heart of the underlying theories for why the party in power struggles in midterms.

And that gives me a little more pause about blowing them off.

If there’s a saying that captures why midterms go so poorly for the president’s party, it’s the idea that “midterms are a referendum, not a choice.” If it’s a referendum, the Democrats are in trouble. After all, President Biden’s approval rating is in the low 40s.

But this year, there’s a pretty good reason to think this won’t just be a referendum: Donald J. Trump.

Consider this: “Donald Trump” still earns more Google search interest than “Joe Biden.” It’s nothing like prior midterms, when the attention was focused all but exclusively on the president. These midterms certainly are different.

Google search interest is a rough proxy for something that’s hard to dispute: Mr. Trump looms over this campaign in countless ways, often distracting the news media, candidates and voters from President Biden.

The emergence of “democracy” as one of the more important issues in the election is almost entirely a function of his presence, whether it’s by promoting “stop the steal” sentiments, endorsing candidates on the right, or fanning fears of election subversion and political violence.

Mr. Trump doesn’t just make it harder for Republicans to make the midterms into a referendum. He has made it less likely that Republican candidates will even try to make the midterms into a referendum. Republican candidates spent the primary season focused on earning the support of Mr. Trump and his supporters, rather than focused on Mr. Biden. It led them far from the classic “check-and-balance” midterms message, in which a challenger promises to work with the president where they agree but block the excesses of his agenda.

The electorate’s instinct to check-and-balance the president is another underlying explanation for the midterm penalty.

In this account, presidents don’t simply lose because it’s a referendum; they lose because a crucial segment of the public wants to moderate the direction of public policy. It’s related to the idea that public opinion is something like a thermostat, in which the public moves to turn down the heat when policy runs too hot in either direction.

The theory helps explain why some of the worst midterm drubbings come after a president pushes an ambitious agenda — like the Republican landslides after Lyndon Johnson’s Great Society, Bill Clinton’s health care push, or the enactment of the Affordable Care Act under Barack Obama. It may also help explain why presidents with less ambitious plans or accomplishments — like Jimmy Carter or George H.W. Bush — have sometimes avoided a rout, even if their parties lost seats.

But this cycle, it’s the Republicans who achieved one of their most important policy objectives — the equivalent of the Great Society or Obamacare — when the Supreme Court overturned Roe v. Wade and fulfilled a half-century-long political goal of the conservative movement.

I can’t think of an equivalent precedent for anything like this. If you can — a good example of when the party out of power achieved the most significant policy change of a president’s first term — feel free to send us an email at dear.upshot@nytimes.com.

Maybe some readers will come up with a helpful analogy. Either way, we’re experiencing something very different from the usual midterm election.

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