Obama's Democrats have long dominated Illinois politics. But Republicans view their man Scott Brown's capture in January of the late Edward Kennedy's seat in Massachusetts as a sign of voter dismay with Democrats in the White House and Congress.
Public opinion polls ahead of Tuesday's party primaries in Illinois show five-term U.S. Representative Mark Kirk likely to win the Republican nomination easily.
Favored to win the Democratic primary and face off Kirk for the vacant seat is Alexi Giannoulias, Illinois treasurer and Obama's basketball-playing buddy.
"The Democratic candidates are second-tier. They're not particularly exciting, not particularly experienced," DePaul University political analyst Michael Mezey said.
Kirk has lent his own twist to Brown's best-known line in the campaign, saying: "This is not Obama's seat, it's the people's seat."
One poll showed Kirk trailing Giannoulias if the two face off -- but only narrowly. That's a far cry from the 62 percent of Illinois voters who cast ballots for Obama against 37 percent for the Republican John McCain in November 2008.
Because Kirk has been in the House of Representatives since 2000, and because of his moderate stances on some issues, he is less able to take advantage of the anti-incumbent fervor among some voters that likely helped Brown.
"Kirk is not the kind of candidate to get the Tea Partiers' blood running," Mezey said, referring to a nascent movement of fiscal conservatives. "He's a moderate, middle-of-the-road candidate. He's been pro-choice, pro-gay rights, anti-gun."
Roosevelt University political analyst Paul Green said: "These Tea Party guys are riding high right now. But Illinois is a coffee state; there aren't going to be a lot of tea drinkers here."
What had once been considered a safe Senate seat for the Democrats, the vacant Illinois seat has become one of five "toss-up" races where Democrats are in danger of losing, according to the Cook Political Report. (CONTINUES HERE)