George W. Bush wasn’t wildly popular either until 9/11. His party then defied all precedent in the 2002 midterm elections. Photo: Erik S. Lesser/Getty Images

One of the implications of Donald Trump’s remarkably poor (for a newly elected president) approval ratings is that it could be tough for him to improve his standing enough to avoid the usual midterm losses for the party controlling the White House. At FiveThirtyEight Nathaniel Rakich puts the problem into historical context:

[T]hree presidents have carried disapproval ratings into their first midterms that were at least as high as their approval ratings: Ronald Reagan, Bill Clinton and Barack Obama. They were also the victims of the three biggest losses in House seats.

Democrats lost 52 House seats in Clinton’s first midterm and 63 in Obama’s. Republicans lost “only” 26 seats in Reagan’s first midterm, but that’s larger than the loss of 24 that would flip the House to Democrats in 2018.

What about the presidents who did a lot better in their first midterm? They had something in common, too: a national-security crisis.

Two of the three presidents with the best net approval ratings in the middle of their first terms were the two whose party lost the fewest House seats — or even gained them: John F. Kennedy in 1962, amid the relief of the Cuban missile crisis’s successful resolution, and George W. Bush in 2002, in the unifying aftermath of the Sept. 11 attacks.

And from the Trump administration’s point of view, W. offers not only the most recent model for a Republican president, but a best-case scenario in terms of approval ratings:

Only George W. Bush [among presidents since Eisenhower] improved his net approval rating from around three weeks into his presidency to his first midterm elections; the net rating for the other eight newly elected presidents decreased by at least 17 percentage points.

In 2002, you may recall, Bush’s party defied every modern precedent by gaining both House and Senate seats in a midterm while controlling the White House. His approval rating was at 67 percent going into those midterms, and there was one and only one reason for that lofty standing: 9/11.

This is why Donald Trump’s regular fanning of fears about terrorism and other national-security threats makes solid political sense whether or not it is justified by objective reality. Does he have a particular problem with women voters? W. did, too, until the “security moms” phenomenon of 2002 all but eliminated the gender gap.

Now it is true that Democrats contributed to W.’s unlikely ascent into an approval rating stratosphere by largely deferring to his national-security leadership after 9/11. It is hard to imagine them giving Trump the same political benefit, though it is also hard to know how they would behave in the wake of a major attack on “the homeland.” But there is no question Republicans from the White House on down will perceive it to be in their interest to keep Americans worried about their security up until and beyond the midterms. How that affects the policies that shape actual events is a question that should worry us all.