The candidates who are faring well in the polls — Ben Carson and Donald Trump — are also good news for Mr. Cruz. In just about any other year, Mr. Cruz would be the worst-case scenario for the party’s establishment. But compared with the likes of Mr. Trump and Mr. Carson, he seems reasonable and conventional. That might let him become a candidate the party could grudgingly accept. His debate performances, especially the one last week, have only helped in this regard.

Mr. Cruz hasn’t been faring particularly well in the polls, but there is a path forward. Even when he seemed to have little or no chance nationally, it was still clear that he could do well in Iowa, a state where nearly half of the Republican electorate is “very conservative,” according to the exit polls. He doesn’t lead there now, but the caucus is still three months off, and he has a large and untapped war chest. Mr. Trump and Mr. Carson might fade, which could help if a disproportionate share of their anti-establishment support goes his way.

If Mr. Cruz finishes well in Iowa, it won’t be hard to envision a serious run for the nomination. He could follow up a win in Iowa with strength in South Carolina and particularly Nevada, another caucus state where half of the G.O.P. electorate is “very conservative.” Soon after come the predominantly Southern states on Super Tuesday, where very conservative voters represent a larger share of the primary electorate than any other region of the country.