Update: The Club for Growth is now buying airtime in Indiana for what will be like be a campaign against Sen. Lugar, according to an operative who follows media buys.

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Sen. Richard Lugar, R-Ind. (J. Scott Applewhite/AP)

Congressional rules allow Lugar to bill taxpayers for Indianapolis hotel stays when the Senate is in session. But he erroneously used taxpayer money for hotel trips to his home state during adjournments, and after an inquiry from Politico, is reimbursing the Treasury $4,500.

The controversy only added to Lugar’s electoral woes — handing his primary opponent, state Treasurer Richard Mourdock, another chance to remind voters that their senator doesn’t actually live in the state in advance of the May 8 vote.

On March 15, an elections board ruled that Lugar could not continue to vote from the Indianapolis home he sold in 1977, forcing the senator to register elsewhere in the state. Lugar is appealing the decision.

And Thursday morning, Lugar got the one of the least helpful endorsements possible. Former Republican-turned-Democratic Sen Arlen Specter, loathed by conservatives for switching parties, encouraged CSPAN viewers to “vote for Dick Lugar”. 

A spokesman for Lugar said that these “non-issue attacks” from Mourdock and allies would ultimately repel primary voters.

 “These are efforts to embarrass Senator Lugar rather than talk about important issues — jobs, gas prices, national security,” said spokesman Andy Fisher. “Here's a respected Hoosier, a statesman, who's been able to get a lot done for the state and the country, and his opponents are doing this.”

The Lugar campaign is up with an ad to that effect:

But cheap shots or not, it has been a very bad couple weeks for the senator. A Democratic poll released this week showed Mourdock closing in on Lugar, with the senator only six points ahead.