John McCain is certainly out of sync with the Republican base on immigration, and he's taken his share of heat for it. But it takes an awful lot of chutzpah for Mitt Romney to attack McCain yesterday in New Hampshire as "pro-amnesty," when Romney is on record just two years ago explicitly describing McCain's position as not being "amnesty:"

This is an issue that came up in one of the debates, and Romney tried to defend his about face on McCain and immigration reform by launching into purposefully detailed and mind-numbing discussion about the "Z Visa" provision of the bill.

It's one thing to switch positions on an issue. It's something else to then turn around and attack people for holding the same position you just held.

Immigration is a potent issue among Republican voters everywhere, so perhaps Romney's attack will work. On the other hand, the attack is so transparently hypocritical it plays directly into the core vulnerability that is undermining Romney's entire candidacy: that he'll say whatever he needs to and change his stance on any position he feels is necessary to win the Republican nomination.