If you covered American politics between 1976 and 2012, you developed a sense of the rhythm of a party primary: A big field of candidates would rise and fall for months as voters — guided by the media — would light upon one, appreciate their strengths, and then discover their weaknesses and move on to the next one. You’d hear talk about the “flavor of the month” and who was “hot” this week. For a manic stretch of 2012, we all believed seriatim that Michele Bachmann, Rick Perry, and Herman Cain were the likeliest Republican nominee.

And if you were honest about it, you’d admit that the media itself drove much of this process. We got interested in a candidate and inflated their prominence, then challenged them more aggressively and dug hard into their record, then moved on to the next one. We, and the voters who cared what we thought, would sort of sip a candidacy, swirl it around our mouths, and spit it out. The candidate who got our collective attention in March 2003, almost by definition, would not be the nominee — at least, not without a dramatic collapse and rebirth. The candidate who won would be the one who built grassroots support in Iowa and New Hampshire, ignited it in December, and rode a triumphant narrative into quickly locking up the nomination. Those were the 10 presidential campaigns, give or take, dominated by what that era called the mainstream media.

And one of the reasons the political press got Donald Trump so wrong is that his campaign didn’t work like that. When we saw his early polls, we thought he was the flavor of the month. But he was the flavor of every month, of every day. His support grew and grew, and his supporters weren’t just trying the idea out: They cleaved to him more tightly. His support didn’t rise and fall. It snowballed.