Donald Trump does a lot of things that are unacceptable, unimaginable, and unexplainable. But his decision to skip the Fox News debate was entirely understandable.

Trump, the supposed outsider in the Republican race, was playing politics in a very predictable and potentially very smart way—as Thursday night’s events in Des Moines illustrated. What this tells us is something important: Trump often seems as if he’s on some bizarrely egocentric political joyride. Perhaps that was the case at the start of this race. But now, he’s making sly moves—and that’s something Republicans and Democrats (who ought not dismiss the billionaire casually) should note.

Trump skipped Thursday night’s Fox News debate in Des Moines, a move that at the start of the 2016 Republican race would, indeed, have been considered unacceptable, unimaginable, and unexplainable.

But anyone who watched the debate without Trump quickly understood why he decided that he was better off across town.

It wasn’t just that Trump’s counter-rally in Des Moines drew an overflow crowd and wall-to-wall coverage on the other cable news networks. It wasn’t just that Trump got to brag about raising millions of dollars for veterans. It wasn’t just that Trump invited excluded GOP contenders Mike Huckabee (the winner of the 2008 Iowa GOP caucuses) and Rick Santorum (the winner of the 2012 Iowa GOP caucuses) onstage at his event, thus linking himself to two old favorites of evangelical voters.

Trump was not just grabbing an opportunity to help himself. He was encouraging the other candidates to hurt one another.

The billionaire is a narrow front-runner in polls of likely Iowa caucus participants and a wide front-runner among New Hampshire primary voters. Trump faces genuine competition in both states from Texas Senator Ted Cruz and Florida Senator Marco Rubio. In New Hampshire he faces additional competition from Ohio Governor John Kasich and former Florida governor Jeb Bush. (Yes, Bush’s Granite State poll numbers have been on a notable upswing in recent days.)

Had he taken the stage with the rest of the candidates, Trump would have taken hits directly from them. He also would have had to stand by while they took shots at one another. They did just that: Cruz took shots at Rubio, Rubio took shots at Cruz, Bush took shots at Rubio, and Rand Paul took shots at everyone.

By skipping the debate, and letting the rest of the candidates argue among themselves, Trump avoided any potential damage—and he made it harder for the other contenders, especially Cruz, Rubio, and Kasich, to build on whatever momentum they might be accumulating as the key tests approach.

Why does this matter?

Consider the latest polling out of Iowa: The Real Clear Politics‘s averaging of recent polls has Trump at 33 percent and Cruz at 26 percent. Anything could happen on caucus night, and, yes, Cruz could still win it, with what is widely viewed as a superior organization. But the polls seem to suggest that Cruz is stalled, or potentially slipping. Several recent polls have Rubio, who got the Des Moines Register endorsement last weekend, catching up with Cruz. So Cruz was ready to rip Rubio, and Rubio was ready to rip Cruz.

That’s perfect for Trump. If Cruz and Rubio are fighting for second place in Iowa, rather than seeking to displace the front-runner, Trump’s under-organized Iowa campaign might just score a narrow caucus win.

If Cruz stumbles and Rubio surges in Iowa, all the better for Trump. Rubio is running poorly in New Hampshire (where his campaign lacks the energy, focus, and numbers of the Kasich and Bush efforts), which means he would have a hard time translating Iowa progress into New Hampshire progress.

Trump expects a win in New Hampshire, and the polls suggest he’ll get it. The only thing that could make that win better is rest-of-the-race chaos—with Bush, Kasich, Cruz, and Rubio all fighting for scraps.

Trump is no fool. He recognizes all of these dynamics. That’s why he skipped a debate on a network that, when all is said and done, will still be friendly to him if his strategies succeed.

No one should be happy with this circumstance. A healthy politics requires a lot of debates and a lot of participation, especially by high-profile contenders.

But, of course, Trump is not practicing a healthy politics.

He’s playing it rough, and ugly, from the start.

Now, he’s also playing it smart.

And if he plays it rough and ugly and smart in the primaries, it would be absurd (and dangerous) to presume—should Trump secure the Republican nod—that he will not play it rough and ugly and smart in the fall.