The Club for Growth backed state Treasurer Richard Mourdock’s primary bid against Indiana Sen. Dick Lugar, giving the GOP upstart a boost against the six-term Senator.

The conservative group’s political action committee endorsed Mourdock today — just four days after the filing deadline for the May 8 primary.

The club first met with Mourdock to gauge his candidacy a year ago, but the group hesitated to give him its support while his fundraising struggled through the subsequent financial quarters. As late as early January, the group’s president, Chris Chocola, told Roll Call the Club for Growth was still monitoring Mourdock’s campaign to see if he was worthy of its backing.

But the Indiana Senate race has remained a top target for the club, which started to run advertisements against Lugar last summer. Chocola, a former Congressman from Indiana, proclaimed “enough is enough” in his endorsement published in the National Review. He wrote the club had “looked for signs that Lugar had changed his ways, but we found none.”

“Richard Mourdock will vote to limit government, repeal ObamaCare, and will help bring back the jobs lost to the Obama’s economic policies,” Chocola said in a statement. “The Club for Growth PAC proudly endorses Richard Mourdock for United States Senate.”

The club’s announcement comes just one day after Lugar’s campaign released an internal poll showing him with a double-digit lead over Mourdock.

The likely Democratic nominee is Rep. Joe Donnelly. Roll Call rates this contest as Likely Republican.