PAC Chairman Philip Blumel (left) and Senate candidate Richard Mourdock (WIBC.com photo: Eric Berman)

A national term-limits organization is dipping a toe in Indiana's U.S. Senate race.

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U.S. Term Limits' political action committee is donating $5,000 to challenger Richard Mourdock.

Mourdock signed the group's pledge four months ago to support a constitutional amendment limiting senators to two terms and representatives to three. Four U.S. House candidates in Indiana have also signed -- Sixth District Republican Bill Frazier, Fifth District Democrat Tony Long, and Fifth District Republicans David McIntosh and Jason Anderson. But PAC chairman Philip Blumel says Mourdock is the only candidate in the country the group is formally endorsing -- he says the group believes the state treasurer is genuinely committed to the amendment, and has an opportunity to defeat six-term Senator Richard Lugar in the GOP primary.

Lugar spokesman Andy Fisher calls the amendment an "insult to voters" -- he says they already have term-limit power through elections. And he's repeating the Lugar campaign's contention that Mourdock can't be counted on to follow through, because of positions he took on other issues in runs for Congress in 1990 and '92 that stray from the conservative line.

In February, the Senate voted 75-24 to reject a nonbinding resolution of support for the amendment. Lugar and Indiana's other senator, Republican Dan Coats, both voted against it.