The National Rifle Association will endorse Sen. Dick Lugar's (R-Ind.) Tea Party-backed primary opponent Wednesday morning, sources with knowledge of the endorsement told The Hill.

Their endorsement of Indiana state Treasurer Richard Mourdock (R) over Lugar could be a body blow to the longtime senator. The NRA is a powerful group popular in Indiana, a state where many Democrats also support the group's policy goals. By making Lugar a target, they could contribute to his downfall.

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Lugar has already had a rough few weeks, after struggling to handle questions on whether he lives in Indiana or Virginia. Lugar has not owned a home in Indiana for decades, and while he survived a legal challenge to his residency, the optics of the fight have done damage to his campaign. He failed in a TV interview to remember what address is on his driver's license, and both Mourdock and Democrats have hammered him on the issue.

Mourdock already has the backing of many fiscally conservative outside groups, including the deep-pocketed Club for Growth, but the NRA's endorsement will give him added support from a new group of conservatives.