Sen. Dick Lugar’s campaign is questioning the validity of a Club for Growth-sponsored poll that showed the Indiana Republican virtually tied with his primary opponent.

“The data released by the Club for Growth does not resemble anything we are seeing,” Lugar political director David Willkie said in a Wednesday statement. “Before commenting on a purely publicity driven poll commissioned by an outside group that has spent hundreds of thousands of dollars against us, we need to know much more about the methodology.”

The club-sponsored poll showed state Treasurer Richard Mourdock with a small advantage over Lugar, 34 percent to 32 percent, in the Basswood Research poll released this week. But Mourdock’s 2-point lead is within the poll’s 4.4-point margin of error.

The conservative, anti-tax organization has not endorsed Mourdock, but its president, Chris Chocola, has frequently criticized Lugar’s record. Earlier this month, the club sponsored anti-Lugar television ads.

“An incumbent who sits at 32 percent in his own party’s primary, and trails a much less known challenger, is in a world of trouble,” Chocola, a former Indiana Congressman, said in a statement. “Senator Lugar is a very decent man, but it’s clear from the poll that after 35 years, Hoosier Republicans are eager for a more conservative alternative.”

About one-third of those polled, 34 percent, said they were undecided about the GOP Senate primary field.

Basswood Research conducted the poll of 500 likely Republican primary voters July 23-24.