Mitt Romney is a famously cautious man, very alert to downside risks. Yet by selecting Paul Ryan as his running mate (assuming the late-night reports are indeed correct) Romney has taken an awesome ideological gamble. This election—which Romney once intended to make a referendum on Obama's record—will now become a referendum on Paul Ryan's bold budget ideas. Why would Romney make such a choice and take such a risk?
1) Like many Republicans, Mitt Romney has been genuinely radicalized since 2008. He has adopted Ryan's ideas as his own and sincerely wishes to campaign on them, and—if elected—govern by them.
2) Romney's internal polling shows that he is not holding the GOP base. Possibly some of his slide in the polls over the past weeks represents leakage from his right flank, not his left. He may imagine that he needs Ryan as his best hope to unify his party.
3) The donors demanded it. Romney is raising huge sums of super PAC money from comparatively few people. The result of this financial strategy is to empower donor preferences—and they may prefer Ryan.
4) Romney may be thinking ahead to after the election. If the Republicans should win in 2012, a House budget chairman Ryan would emerge as the effective leader of the Republicans in the House. Romney may calculate that it's safer to have Ryan inside the administration under his control than acting as an independent power on Capitol Hill.
5) Romney may just have crumbled and yielded to pressure.
When I air skepticism about this pick, I get push-back from overjoyed conservatives. On Ryan's behalf, it must be said: he's intelligent, serious-minded, and refreshingly sincere. In character, Paul Ryan is everything one would want in a national political leader.
Yet it's also true that Ryan has been pushed forward by people who do not much like or respect Mitt Romney, precisely with a view to constraining and controlling a Romney presidency. By acceding to that pressure—for whichever of the five reasons above, or for some sixth or seventh reason—Romney has transformed a campaign about jobs and growth into a campaign about entitlements and Medicare. Romney will now have to spend the next months explaining how and why shrinking Medicare after 2023 will create prosperity in 2013. Economic conditions are so tough—the Obama reelection proposition is so weak—that Romney may win anyway. But wow, the job just got harder.