WASHINGTON (AP) — The prominent conservative group Club for Growth is endorsing Indiana Treasurer Richard Mourdock in his bid to unseat longtime GOP Sen. Richard Lugar.

The national group announced its endorsement Tuesday. President Chris Chocola tells The Associated Press his organization is backing Mourdock in the May 8 primary because he is a strong conservative on economic issues and because Lugar can't be counted on.

The Club for Growth ran television advertisements last summer attacking Lugar but had previously declined to back Mourdock. Chocola says Lugar's decision to vote against a permanent ban on earmarks recently was the final straw for the group.

The endorsement is likely to provide Mourdock a fundraising boost. It also gives him an important nod from a key conservative group as he courts GOP primary voters.