The first mystery of the year was how Donald Trump won his party’s nomination, but more important, why 16 others, including popular governors and senators, lost. The answer is simply that all the others thought the key to the Republican base was ideology. Some, such as Senator Ted Cruz of Texas, styled themselves as the purest and most adamant of conservatives, others as just practical enough to deliver on conservative goals and one (Gov. John Kasich) as sort of a moderate. None of them clicked with the Republican base, simply because ideology wasn’t what motivated the base. It was always about identity, about them and us. Only Mr. Trump had that key.

Consider immigration, the concept that drove both the Tea Party and the Trump campaign. For most of the long campaign, the media thought that it was about immigration policy: comprehensive immigration reform versus border security and deportations. The Republican “autopsy” from 2012 concluded that Republicans should support immigration reform. But it turns out it was always just about immigrants, as in, people who aren’t like us, not policy.

That’s why Trump supporters were unmoved by reports that Melania Trump had worked in the United States without authorization, and it’s why Mr. Trump, in a late rally in Minnesota, declared that the state had “suffered enough” from the presence of Somali immigrants, a well-settled middle-class group in the state for more than two decades. It’s why Mr. Trump found his strongest support not in areas most affected by immigration but in aging states with the lowest number of foreign-born residents, such as Ohio, Iowa and Wisconsin, where immigration is mostly a distant symbol of otherness.

Ideology had formed a kind of a comforting curtain around the more intractable divides of race and identity. Ideological conflict, as deep and irresolvable as it often seems, at least in theory, lends itself to persuasion and compromise, such as President Obama’s long quest for a “grand bargain” on spending and taxes. Ideology can help structure people’s engagement with politics, giving them clear preferences organized around a few core values.

But ideology can also be hard work — most people don’t have the time or inclination to decide if they are “liberal” or “conservative,” and what that means, or to fight about it.