Lugar isn't eligible to vote in IN, has voted illegally in the past.

[Southern Senator North Carolina Yankee]

The arguement of positive versus negative campaigning is one of the most vague and likely misleading arguements to make. The standards constantly shift and in some cases it is absolutely essential. In order to defeat a Lugar you have convince voters that he has become out of touch; otherwise, why would anybody vote them out. Lugar's job is to refute that convincingly. To deny the ability of challengers to frame a race on those terms would produce effects that would be the equivalent of a reverse term limit if such were possible and ensure someone like Lugar did in fact become out of touch, as there would be no incentive not to.