This guy may be thrilled with Trump’s performance, but he and his friends may not be enough for Trump’s party. Photo: Brooks Kraft/Corbis via Getty Images

An awful lot of what the Trump administration and most congressional Republicans seem preoccupied with doing this year revolves around keeping the president’s “base” happy. And it’s worked pretty well, as multiple polls showing Trump voters generally satisfied would tend to indicate. But although paying attention to one’s own past voters is typically a good idea, it’s not enough to guarantee a winning Republican performance in 2018. As Harry Enten demonstrates via some standard history and arithmetic, the Trump base is too small to overwhelm the majority of Americans who are not happy with his performance unless turnout patterns are very strange. Here’s his key argument:

The president’s party has lost at least 83 percent of voters who disapprove of the president’s job in every midterm since 1994. In none did the president’s party win more than 87 percent of those who approved of the president’s job. These statistics are not good news for Republicans if Trump’s current approval rating (40 percent among voters) and current disapproval rating (55 percent) holds through the midterm. Even if Trump’s Republican Party wins the recent high water mark of 87 percent of those who approve of the job the president is doing and loses only 83 percent of those who disapprove, Republicans would still lose the House popular vote by 7 percentage points. That could be enough for them to lose the House.

Now there are some qualifiers for that analysis. At Enten himself notes, House Republicans did marginally better than Trump in 2016, so they might do marginally better than a breakdown of voters who do and don’t approve of Trump’s job performance would suggest. Just as importantly, we have no idea yet whether the apparent “enthusiasm gap” benefiting Democrats right now will offset the traditionally poor midterm turnout patterns of demographic groups currently leaning Democratic. Similarly, most polls measuring early assessments of Trump’s job performance do not include screening for likelihood to vote; many do not even screen for voter registration. So they may understate Trump’s popularity among the people who are actually going to show up at the polls next year.

Having said all that, a president as polarizing as Donald Trump — one who has, moreover, worked to guarantee bad press for himself by endlessly attacking the media and defying all conventional ideas of presidential behavior — is not going to make it easy for Republicans to minimize the usual midterm trend against the party that controls the White House. Presidential job approval is highly correlated with midterm elections results; the only two times since World War II when the White House party has gained House seats in a midterm (the back-to-back elections of 1998 and 2002), the president had very high job approval ratings. It’s a lead-pipe cinch Republicans will lose seats next year, and the only question is how many. So they’d best find a way to make nice with voters who have not and will never wear those red MAGA hats.