First, he isn’t Huckabee or Santorum. They were true insurgents, desperately underfunded candidates who staked everything on Iowa and then lacked a plan to follow through. Cruz has the money and the organization that they lacked, and notwithstanding his “Duck Dynasty” endorsement and Senate enemies, he has a network of elite support that can carry him through a long campaign.

Second, the calendar promises him momentum. South Carolina is a good state for him, and then the large so-called S.E.C. primary looms on March 1, rich in evangelical votes. The S.E.C. states aren’t winner take all, so Cruz can’t build an insurmountable delegate lead even if he runs the table. But on the morning of March 2, the media may start covering him as if he’s the front-runner.

Third, he’s already consolidated most of the constituency he needs to go deep into the campaign. Rand Paul’s departure, in particular, is a reminder of how effectively Cruz had already cut into his libertarian, anti-Washington and anti-interventionist base. Rubio hasn’t yet done the same to Jeb Bush and the rest of the center-right pack: His Iowa finish helps, but unlike Cruz, he needs to prove something in New Hampshire to start pushing major rivals out of the race.

Then finally, if Rubio does consolidate support, Cruz has clear lines of attack against him.