Donald Trump approaches a horse from behind.

Donald Trump led the field with support from a whopping 24% of Republican respondents to a Washington Post/ABC News poll conducted late last week, beating Scott Walker by 11 points. I bet you didn’t think you’d be pulling for Scott Walker in 2015, did you? But the Post seems to have buried the lead in its story on the poll: although Trump polled very well Thursday and Friday, his support plummeted Saturday night, after the media widely reported his remarks about John McCain. It seems Trump has defined some contours of the contemporary Republican Party. You can call Mexicans rapists, but you cannot attack a veteran.

This turn of events promises to answer a vexing question: What is Donald Trump good for? The rest of this post proceeds from the assumption that he will not be president, because at least 51% of registered voters are not stupid assholes. Sixteen months before the general, one in four respondents to polls might be. But if Trump wins the Republican nomination, to say nothing of the presidency, I will convert Combat! to a mommy blog.

So what’s the point? Unless I miss my guess, Trump knows he’s not going to be president as well as we do. He hasn’t hired aides or assembled state-level organizers and policy wonks the way a serious candidate does. He seems to be campaigning to restore the kind of celebrity he enjoyed in the 1980s. That explains how Trump for President is good for him, but it doesn’t do much for us—or didn’t, until last weekend.

What if Trump functioned as a kind of sonar, constantly making noises that were useless in themselves, but whose echoes revealed the contours of a previously unknown world? I’m speaking, of course, of the desires of contemporary conservatives—a realm as enigmatic and haunting as any deep-sea trench.

Remember when the Tea Party was a vitally important movement nobody knew anything about? Political analysts covered it relentlessly but anecdotally; it was a movement with no leaders, no articulated ideology, and no quantified demographics. Maybe there were enough of them to constitute a third party, or maybe the whole thing was a news-cycle bogeyman.¹

Like one of those camera robots we drop into a flaming oil well, Donald Trump solves this problem. The unit is expendable,² but the information it sends back is invaluable. If you told me three months ago that Republicans would respond positively to the sentence “Mexicans are rapists” but negatively to “John McCain is not a hero,” I would have accused you of cynicism. But the last month of the Trump campaign seems to have proved it.

More than one Republican strategist is concerned that Trump is hurting the Republican brand. Perhaps he is, although I submit that if you are not among the 24% of likely primary voters who claim to support his candidacy, you disregard him so thoroughly that he doesn’t reflect on his party at all. But I think pollsters and politicos should embrace him as a test candidate. His wildly fluctuating poll numbers and knack for focusing his candidacy on one statement at a time—generally by swamping the news cycle with the audacity of a single remark—make him a serial test of hypotheses, a way to isolate variables among the mysterious conservative base.

Lately, the results of those experiments have been kind of depressing. For example, Trump-bot has confirmed that race-baiting works, at least in the unserious early weeks. But he also found the depth of the sea floor when he insulted McCain’s POW experience, a flippant remark that backfired immediately. Now that the Trump campaign is about dismissing the torture of a US senator instead of hating Mexicans, the bloom is off the rose.

I can’t wait to see what the Trump campaign is about next week. Probably, he will return to the warm currents of attacking President Obama. The birther thing is played out at this point, so maybe Trump will suggest he is a secret Muslim. There’s also tax reform, which seems like a difficult thing to be audacious about. But Trump-bot will find a way. It’s what he’s programmed to do.

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