When presidential debate moderators disclaim their own factual knowledge, and refuse to correct erroneous or dishonest answers, it falls to other candidates to step into the breach.

But what happens when other candidates are too ill-briefed to correct their competitors, or too tempted by the incentive to out-deceive or out-exaggerate them, to keep things tempered?

The debate in Milwaukee on Tuesday night met just about every Republican demand: open-ended questions, pliant moderators, complacent candidates. But it did not wear well. Jeb Bush, an exception to this overall dynamic, tried to bring a modicum of sobriety to the discussion by scolding his unrealistic adversaries. “They’re doing high-fives in the Clinton campaign right now when they hear this,” he said. Republicans should have listened to him.

When Donald Trump promised (again) to round up and deport millions of unauthorized immigrants, both John Kasich and Bush stepped in to point out how implausible and inhumane such a plan would be. But arguably Kasich and Bush are stuck in the polling doldrums precisely because they take a realistic view of immigration policy.

Ted Cruz ultimately chimed in on Trump’s behalf with a canned response—“The Democrats are laughing, because if Republicans join Democrats as the party of amnesty, we will lose”—and was met with tremendous applause.