Jonah Goldberg of National Review Online explores the possibility.

Of the nine sitting presidents who’ve sought re-election since 1964, five faced opponents from their own party.

More significantly, there’s ample demand for a primary challenge. A new NPR-PBS-Marist poll found that Republicans are essentially divided evenly on the question. Asked if they’d like to see a challenge, 44 percent of respondents said they’d like to see a challenge, 45 percent said no, and 11 percent said they were unsure.

This doesn’t necessarily mean that nearly half of all Republicans want to see Trump defeated in the primaries. According to a recent Des Moines Register poll, Trump has an 81 percent approval rating among registered Republicans in Iowa, and 67 percent of them say they’d vote to re-elect him.

But almost as many Republicans (63 percent) said they would welcome a challenger in the Iowa caucuses. Polls show similar attitudes in New Hampshire.

For Trump’s biggest fans, this is crazy talk. But most of Trump’s biggest fans are old, and they tend to rely on traditional conservative media outlets for their understanding of the political landscape.

Among young people generally, Trump’s approval rating hovers at around 30 percent. Last year, an Axios survey found that more than 80 percent of Republicans and Republican “leaners” between the ages of 18 and 24 wanted to see Trump challenged in a primary, compared with 74 percent of Republicans over the age of 65. According to the NPR-PBS-Marist poll, a majority of Republicans under the age of 45 would like to see a Republican challenge Trump.