Indianapolis Business Journal is reporting that Lugar has sent out a call for Independents and Democrats to cross party lines and ask for a Republican ballot in the primary. He asks they will then use their vote to help him defeat challenger Richard Mourdock.
The problem with that is that it may be illegal for voters to cross the party lines as Lugar is asking them to do. According to Indiana law, you can only pull a party's ballot in a primary if you cast at least half of your votes for that party in the previous general election, or if you intend to cast at least half your votes for that party in the next general election.
Independents may not be breaking the law very often by pulling a primary ballot that they normally wouldn't. Democrats and Libertarians who pull a Republican ballot for the sake of the Senate or Presidential race, or some other reason, are clearly in violation and are committing voter fraud.
Is that an enforceable law? No, not at all. The only way the law could ever be enforced is if we moved away from a secret ballot. That, of course, is never going to happen.
But whether it is an enforceable law doesn't change the fact that it is the law, and Dick Lugar is asking people to break it for his own political gain.