He lied tonight. Money quote:
Mitt Romney said, "I've never voted for a Democrat when there was a Republican on the ballot." … He voted for Senator Paul Tsongas, a Massachusetts Democrat, when he ran in 1992 for the presidential nomination against Bill Clinton, among others. That was the same day, and the same year, that President George H.W. Bush and Pat Buchanan were on the Republican ballot.
As an independent, Mr. Romney could have voted in either party's primary, and apparently chose to vote for the Democrat.