It has been 37 years since the last time an incumbent president drew a serious primary challenger — Ted Kennedy against Jimmy Carter — and 25 years since Pat Buchanan made noise as a protest candidate in New Hampshire against George H.W. Bush. But if someone who had slept through the 2016 campaign were suddenly awakened and given a few key facts about the state of Donald Trump’s administration, they would instantly suggest that he should expect not just a Republican challenger in 2020, but one with decent prospects of success.

Those facts start with Trump being reduced to a 38 percent approval rating just nine months into his presidency, despite solid economic trends and no foreign crises worse than saber rattling. They include the ongoing investigation into his campaign associates’ ties to Russia, which has already produced indictments, and his Carteresque failures on domestic policy, despite Republican control of Congress. And they include the quiet fear and loathing Trump continues to inspire among Republican elites — including the former Republican president who recently slammed him by implication, and the two Republican senators who just questioned his fitness for his office.

But unlike our fictional Rip Van Winkle, we were all awake in 2016, and so this litany of weaknesses is not enough to vindicate Matt Bai, the longtime political correspondent, who recently called a serious primary challenge “inevitable.” Instead the experience of ’16 points to a different interpretation of the facts — that having failed to stop Trump when he was eminently beatable, the ranks of Republican politicians are unlikely to throw up a serious challenger now that he has consolidated partisan support.