(CBS News) Republican Richard Lugar has represented Indiana in the Senate for six terms, but Hoosier Republican voters may be ready for a change.
A Howey/DePauw University poll conducted Monday and Tuesday shows Lugar trailing his primary challenger, Indiana Treasurer Richard Mourdock, by 10 points among likely Republican primary voters. Mourdock leads Lugar 48 percent to 38 percent.
Twenty-two percent said they were undecided, and another 11 percent said they could change their mind before the May 8 primary. But even among those who had "definitely" made up their mind, Mourdock led 37 percent to 30 percent. The poll had a margin of error of 3.7 percent.
A number of Tea Party groups -- including national groups and some from Indiana -- have gotten behind Mourdock, and the challenger does have the support of very conservative voters. A plurality of primary voters, 44 percent, identified as "very conservative," and 63 percent of those voters favored Mourdock.
Still, the poll shows that Mourdock also has a slight edge among voters who identify as "somewhat conservative" (he takes 43 percent to Lugar's 41 percent).
"While the Tea Party and other national groups got into this race because of what they consider to be Lugar's liberal transgressions, it appears that a bigger issue for GOP primary voters is simply his longevity," pollster Christine Matthews told Howey Politics Indiana. "It is a very difficult environment to be running as a 35 year incumbent."
Indeed, 23 percent of Mourdock supporters said they were mainly supporting him because Lugar has been in office too long. Another 16 percent said the main reason was that it's time for a change.
Lugar is the top Republican on the Senate Foreign Relations committee and one of the most senior members in the Senate. He's Indiana's longest-serving senator.
Over the years, however, he's become more of a Washingtonian than a Hoosier. Lugar sold his Indianapolis home in 1977 and has since lived in the Washington, D.C. area. In March, a local election board voted that Lugar, but the senator resolved that issue by agreeing to switch his voter registration to his family farm in Marion County, Indiana.