Donald Trump isn’t going to be the Republican nominee.

Six months ago, that was a truism. Three months ago, it was the conventional wisdom. Now it’s an assertion that inspires sympathetic glances, the kind you get when you tell friends that you think your new personal-investment strategy is sure to beat the market.

I know you really want that to be true, the glances say, but you just might be kidding yourself.

It’s easy to see why people are starting to think this way. Trump has led the national polls since last summer, and not by a little. Apart from the Ben Carson bubble, nothing has dented his advantage: It’s actually expanded over the last month, and nobody in the G.O.P. seems to have a coherent plan to cut into his support.

“Based on polling data,” Sam Wang of the Princeton Election Consortium wrote this week, “Donald Trump is in as strong a position to get his party’s nomination as Hillary Clinton in 2016, George W. Bush in 2000, or Al Gore in 2000.”

“TRUTH BOMB,” wrote Politico’s Mike Allen, the insider’s insider. “If you think voters will suddenly get serious — and that Trump is a ‘lampshade candidate’ who’ll eventually wear out his welcome — you’re running out of time to be right.”