President Barack Obama stars in an ad running in Illinois on behalf of his potential successor, state Treasurer Alexi Giannoulias. The new ad strings together video of Obama’s appearance with Giannoulias in Chicago in August and counters Republicans’ characterization of Giannoulias as a “mob banker.”

“On his very first day in office, Alexi enacted sweeping ethics reforms,” Obama says in the ad. “He’s proven himself as someone who isn’t afraid to stand up to special interests.”

Although Obama isn’t as popular in Illinois as he once was, just more than half of Illinois voters approve of the job he has done so far, according to a poll taken for the Chicago Tribune and WGN from Aug. 28 to Sept. 1. The Illinois Senate seat has extra symbolism since Obama held it until he was elected president in 2008. As the state’s junior Senator, Obama endorsed Giannoulias for state treasurer in 2006.

The same poll showed Giannoulias tied at 34 percent with Republican nominee Rep. Mark Kirk. LeAlan Jones, the Green Party candidate, was the choice for six percent of voters. The poll had a margin of error of four points.

The race to replace appointed Sen. Roland Burris has been hard-fought. Kirk has accused Giannoulias of shady dealings while he was working at his family’s bank and of mismanaging an education savings fund during his time as treasurer. Kirk has also tried to tie the Democrat to party leadership in Congress.

Giannoulias, on the other hand, has questioned Kirk’s military record and has picked apart his legislative record, including his support for the Iraq war.