Embattled Sen. Dick Lugar (Ind.) has had a rough couple of weeks, and a new poll underscores just how much trouble he is in against state Treasurer Richard Mourdock in the GOP primary next month.

Lugar led Mourdock 42 percent to 35 percent among likely GOP primary voters, according to the Howey/DePauw Indiana Battleground Poll released today. While the poll showed Lugar with a single-digit lead, 42 percent is a dangerously low number for a veteran lawmaker and it underscores just how competitive Lugar’s first tough re-election battle has become.

Indiana has an open primary, and therefore, independents and Democrats can vote in the May 8 contest. Lugar and Mourdock ran even among self-identified Republicans in the poll, which suggests the Senator’s saving grace lies with independents. Lugar led among independents and voters who said they lean Republican, 52 percent to 26 percent.

If Mourdock is the nominee, the poll showed Democrats could compete for the seat. The likely Democratic nominee, Rep. Joe Donnelly, was tied with Mourdock at 35 percent in the survey. By comparison, Donnelly trailed Lugar, 29 percent to 50 percent, in a hypothetical matchup.

The poll was performed by Bellwether Research & Consulting, a GOP firm, and Garin-Hart-Yang Research Group, a Democratic firm. They conducted the poll of 503 likely GOP primary voters March 26-28. It had a margin of error of 4.5 points.