Sometimes Iowa eliminates candidates quickly: Last Monday night, Democrat Martin O’Malley and Republican Mike Huckabee announced immediately that they were out. Rand Paul and Rick Santorum soon followed suit.

Sometimes it happens more slowly. Iowa Republicans just sent a strong signal to New Hampshire and national Republicans that only two candidates remain viable: Ted Cruz, who finished first with 28 percent of the vote, and Marco Rubio, in third place with 23 percent, just barely behind Donald Trump.

Is it an absolutely definitive signal? No; in politics unlikely things can always happen. But no candidate has been a hopeless also-ran in the Iowa caucuses and rebounded to come anywhere close to a presidential nomination, and there’s no reason to expect John Kasich, Jeb Bush, Carly Fiorina, or Chris Christie to seriously contest the nomination after this point.

Donald Trump? We don’t know whether his polling numbers elsewhere will fall off as the campaign goes to other states, nor do we know whether losing in one place will destroy his message of being a winner. Both seem very possible, but we’ll have to wait and see. If not, however, his overall unpopularity among Republicans still severely limits his chances as the field narrows further. Certainly, he’s going to need more than a quarter of the vote (what he received in Iowa). Put it this way: To win, Trump needs this to be an “everything is different this time” election, and Monday was strong evidence that the normal political rules apply.

We’ll see now how New Hampshire Republicans react tomorrow to the signals coming from Iowa. Will moderate and mainstream conservatives jump on the Rubio bandwagon? Will Ted Cruz pick up serious support? It certainly wouldn’t be surprising if support for Bush, Kasich and Christie dips. Either way, national Republicans will almost certainly react to the signal from Iowa by pouring resources into the Rubio campaign.

One more thing on the Republican side. If almost no Republican Party actors want Trump to win, and a majority also don’t want Cruz to win, will they put pressure on Bush and other also-rans to stop attacking Rubio?

Put it all together and one can say: Yes, Iowa only eliminates candidates, but if we’re down to only two with a plausible chance at the nomination, well, that’s a lot of eliminating.

There’s less to say on the Democratic side. Hillary Clinton squeezed out a very narrow victory over Bernie Sanders. Nothing much changed. The Sanders showing was impressive, and there’s no reason to expect his big lead in New Hampshire to dissipate, but there’s still little reason to expect him to win the nomination.

All that said: There’s a long way to go — 49 states, plus Washington D.C., Puerto Rico, and more! Again, something unexpected can happen on either side. But last Monday was a step away from “this time it’s different” on both sides. And that suggests — but certainly doesn’t prove — that the rest of the race will be predictable as well.

Jonathan Bernstein is a Bloomberg View columnist.