According to the latest Howey/DePauw University poll released last Thursday, Democrat Joe Donnelly leads 40 to 38 percent among likely voters -- that's within the margin of error.
Experts say the third party candidate for Senate may be having a negative affect on Mourdock. The poll shows seven percent of likely voters support Libertarian candidate Andrew Horning.
"Most people are going to speculate that it's benefitting Donnelly," says Andy Downs of the Mike Downs Center for Indiana Politics at IPFW. "More than likely a chunk of [Horning supporters] are the people who would have voted for a Republican candidate if there were two options."
As for the other races in the DePauw poll, Mitt Romney has a 12 point lead over President Obama in Indiana. In the Governor's race, Republican Mike Pence is up 13 percent over Democrat John Gregg.