In theory, Ted Cruz’s best states are behind him. But at the Detroit debate, Cruz was clearly the class of the field and it's clear that no one should count him out as the delegate race moves into its next phase.

The delegate math is complicated, but the basic gist goes something like this: Donald Trump has a commanding lead at the moment, but it is not a given that he will reach the 1,237 threshold he needs to clinch a majority. Simply put, Trump has failed to break through the ceiling of support he's held since New Hampshire even as the field has consolidated. While he will be helped by winner-take-all states, where he can sweep full slates of delegates even with his plurality, he may be hurt by closed-primary states, where only Republicans vote. So his path is more challenging than it appears.

Cruz's path is more challenging still. But tonight's strong performance can only help Cruz—both with voters and with the party regulars who would play a big role in deciding the nominee should there be a brokered convention.

What Cruz did at the debate was make three parallel cases:

1.) Trump is a fraud who can't be trusted to keep his word.

2.) Trump is not either conservative or Republican in any meaningful way.

3.) Trump actually is the corruption that he decries.

He advanced these arguments not one at a time, but by interweaving them with specific attacks:

* He positively crushed Trump on the use of foreign labor at Mar-a-Lago. He didn't just bring up the fact that hundreds of applicants applied for these jobs but that Trump prefers to hire foreigners instead, but included Trump's line from the last post-debate interview where he claimed that these were jobs American workers couldn't and wouldn't do.

* He thoroughly prosecuted Trump on the question of Trump's off-the-record New York Times interview, which Trump steadfastly refuses to release.

* At the end of the segment on Trump University—where Trump's best defense was telling voters that they should "wait a few years" to see whether or not he committed fraud, Cruz flashed in with a rapier: "Megyn, let me ask the voters at home, is this the debate you want playing out in the general election?" It was brutal.

* When Trump went to his poll numbers—as he always does—Cruz was ready. Trump touted a terrible CNN poll showing him at 49 percent support. Cruz waited for Trump to double down and defend the integrity of the poll. And then he noted that this same poll also showed Trump losing to Clinton and Cruz beating her.

* When the Second Amendment came up, Trump made a gauzy statement of general support. Cruz then dropped the hammer:

It is easy for political candidates to have rhetoric and say, "I support the Second Amendment." But you cannot say that and at the same time say what Donald just said, which is that on the question of Supreme Court nominees he wants to compromise and reach a middle ground with Harry Reid and Chuck Schumer. That's what he said in the last debate. . . . And I would point out, Harry Reid and Chuck Schumer are both Democrats that Mr. Trump has written checks to repeatedly. Any justice that those two sign off on is going to be a left-wing judicial activist who will undermine religious liberty, and we are one vote away from the Heller decision being overturned, which would effectively erase the Second Amendment from the Bill of Rights. Amendment rights, but when you say you'd compromise with Harry Reid, you put that in jeopardy.

* Cruz's most devastating line was probably this summation:

I understand the folks who are supporting Donald right now. You're angry. You're angry at Washington, and he uses angry rhetoric. But for 40 years, Donald has been part of the corruption in Washington that you're angry about. And you're not going to stop the corruption in Washington by supporting someone who has supported liberal Democrats for four decades, from Jimmy Carter to John Kerry to Hillary Clinton. You're not going to stop the corruption and the cronyism by supporting someone who has used government power for private gain.

The question is what Cruz's performance gets him. Maybe nothing. The terrain ahead could simply be too tough. But maybe not.

Trump remains vulnerable. Marco Rubio's brawling attacks on Trump have served as a force multiplier for Cruz's more surgical prosecutions of the frontrunner. It is objectively true that no presumed nominee has ever been so completely dominated—on matters of fact, issues of policy, and modes of conduct. If any other presidential candidate in the modern era had turned in a performance like Trump's tonight—let alone two of them, consecutively—people would be writing obituaries not just for his campaign, but his career.

Cruz's performance was so forceful and at one point, Trump was reduced to a spitting, orange-faced rage, calling him "Lyin' Ted." Lion Ted was more like it.