It’s over: CNN estimates that Barack Obama has won enough delegates to clinch the Democratic nomination for president in 2012.

Oh—the Republicans? OK, I’ll concede that contest is getting close to over as well. Mitt Romney will almost certainly be the GOP nominee. Rick Santorum is entitled to stay in the race, and to offer voters in the remaining states an alternative. But it’s probably time for him to do what Mike Huckabee did in similar circumstances in 2008—basically to stop attacking the almost inevitable nominee, and instead to adjust his own message going forward to a positive and issues-based one.