It can be amazing how small things — a couple of points on a primary night, an appearance or debate gone wrong — can change the trajectory of a nomination battle. It may be that we’ll look back at Rubio’s New Hampshire debate stumble as one of those moments.

It is certainly possibly that Donald Trump would be romping no matter what. But here’s the counter-factual: If Rubio had won his exchange with Chris Christie that night, many people would have said he won the debate, and he probably would have finished a fairly strong second. That may have pressured Jeb Bush and John Kasich to drop out prior to South Carolina (although based on current evidence, maybe Kasich would never get out no matter what). If those guys had dropped, then Rubio may well have been truly competitive in South Carolina and at least made it a close race, denying Trump his current, juggernaut-like momentum.

But it’s all history now. Rubio still has a path, but it is narrow and depends a number of things not in his control breaking the right way.