During his first run for the Republican presidential nomination, Mitt Romney claimed that his vote for Paul Tsongas in the 1992 Democratic primary was an attempt to benefit the GOP:
"In Massachusetts, if you register as an independent, you can vote in either the Republican or Democratic primary," said Romney, who until he made an unsuccessful run for Senate in 1994 had spent his adult life as a registered independent. "When there was no real contest in the Republican primary, I'd vote in the Democrat primary, vote for the person who I thought would be the weakest opponent for the Republican."
In his fight for the Michigan primary, Rick Santorum has adopted a similar strategy-asking Michigan Democrats to vote for him, and tip the scale against Romney.
Naturally, Romney isn't too happy about this:
"Sen. Santorum did something today which I think is deceptive and a dirty trick," Romney said on Fox News. […]
As for the Santorum campaign's robo calls, however, Romney said his rival's strategy is "confusing" and a "new low in this campaign."
Obviously, Romney was acting as a private citizen versus Santorum's status as a presidential candidate, still, it's hard not to be amused by the situation.