In the last six weeks, Lugar's faced an onslaught of questions from opponents and the media about his residency. He lives in northern Virginia but is registered to vote in the Hoosier state at the address of a home he sold in 1977. The state has ruled that he is eligible to run for reelection but a county elections board ruled last week that he is not eligible to vote.
Lugar has outraised Mourdock, whose fundraising has lagged throughout his campaign. He's also outspent him on TV. But in recent weeks, Mourdock has been cobbling together a coalition of influential supports including the anti-tax Club For Growth and the National Rifle Association.
A National Research poll conducted for Lugar in early February showed him leading Mourdock 55 percent to 30 percent.
The Donnelly campaign poll of 500 likely Republican primary voters was conducted by Global Strategy Group from March 12-15 and carries a margin of error of +/- 4.4 percentage points.