Now that everyone is talking about the Republican Party's youth voter problem, let's check in with the three youngest 2016 Republican hopefuls:

1. Marco Rubio is threatening to vote against his own immigration bill. If he does that, it'll be impossible to explain to voters in three years' time.

2. Based on an e-mail I got earlier today, Ted Cruz is really tying his name to the "abolish the IRS" movement. This creates a problem similar to Rubio's: Once the outrage over this IRS scandal dies down, Cruz won't be able to explain to mainstream voters in four years why he made a video calling for the end of the IRS. It'll look insane to all but the craziest teabaggers.

3. And as for the third young guy with 2016 Republican presidential prospects, it's fair to say in retrospect that a lot of the heat around Rand Paul dissipated after his disastrous speech at Howard University.