If Lugar is not considered eligible to vote, he should be disqualified as a candidate since this would mean he is not a resident of IN. If by some dreadful chance he wins renomination, Mourdock should sue to have him removed from the ballot (perhaps he should now).
The sole residency requirement for U.S. Senators and Representatives in the U.S. Constitution is that the person be an inhabitant of the state *when he is elected*. There are state laws, of questionable constitutionality, that impose longer residency requirements for U.S. congressional candidates; I don’t know what Indiana law provides, but surely Lugar can establish residency before the primary, not to mention far before the election.
Lugar’s residency kerfuffle is a great political issue, but a lousy legal issue. Mourdock should just keep hammering away at Lugar for being out of touch, not conservative enough and a Beltway insider, and beat him in the primary, or else we’ll be stuck with Lugar for 6 more years.
This could be what enables Richard Mourdock to break through. So often, it’s the local and parochial issues that cause turnover more than national trends.