This is the point in the column when I would normally signal, subtly or clumsily, whose vision I find more attractive over all. But the reality is that I’m divided. I admire Paul’s outreach to minority voters, and I was very skeptical of the immigration bill Rubio shepherded through the Senate last year. But I have agreed with practically every domestic policy stance the Florida senator has taken since, and his reform agenda seems more sensible on substance and more plausible as politics than Paul’s more stringent libertarianism.

But then on foreign policy my sympathies reverse. Paul’s ties to his father’s more paranoid worldview are problematic, but the realism and restraint he’s championing seem wiser than the G.O.P.’s frequent interventionist tilt. To imagine Rubio as a successful foreign policy president, I have to imagine an administration in the mold of Ronald Reagan’s, where hawkish rhetoric coexists with deep caution about committing U.S. ground troops — and I think there’s reason to worry we’d get incaution and quagmire instead.

I suspect that the Republican electorate would also have mixed sympathies … and that is exactly why the party should want to see these men debate. Maybe that debate would end with one victorious and the other clearly vanquished; maybe it would encourage a kind of partial synthesis, perhaps offered by a savvy rival like Christie. But however the debate turned out, it would involve exactly the issues the Republicans need to work through before they’re given control of the White House once again.