Donald Trump has had a rough couple of weeks. He said he supported punishing women for abortion and then walked it back; his campaign manager was arrested on a charge of battery; he retweeted an unflattering picture of his main opponent’s wife, Heidi Cruz.

And the polls show him trailing by a wide margin in Wisconsin, which holds its primary on Tuesday. For some people, it’s a sign that Mr. Trump is finally losing ground.

But his problem in Wisconsin is mainly about the state’s demographics, not self-inflicted wounds. Even a 10-percentage-point loss there wouldn’t necessarily indicate any shift against him.

The state has always looked as if it would be one of Mr. Trump’s worst. This was true even before the primaries began. Polling by Civis Analytics and Marquette Law both showed Mr. Trump faring much worse there than nationally, just as was the case in neighboring Iowa, where he wound up losing to Ted Cruz.