This will have positive consequences. First, it will allow voters to differentiate between the candidates just as they begin to pay very close attention to the race. If you think the key problem facing the country is terrorism, then the dispute between Rubio and Cruz is the central one.

Cruz says ISIS can be defeated from the air. Rubio says the only way to destroy ISIS is to seize the territory it has occupied. Cruz says the use of metadata to monitor phone traffic is unnecessary. Rubio says it is crucial. These are maybe the two smartest men in American politics right now, and the argument they are having and will continue to have will help shape the election even if neither wins the nomination.

The same is true on immigration. If it’s your central concern, Rubio probably makes you uneasy. But he has said he was wrong to push for a massive immigration-reform package, and says he continues to favor a path to legalization. Cruz says he opposes legalization — but is being cagey and slippery when it comes to his past support for it.

Can Rubio be trusted on the issue if he was wrong on it before? Can Cruz be trusted on it if he isn’t being honest about his own history when it comes to the issue?