Hillarysworld

Photo by: David Banks
U.S. Rep. Mark Kirk, R-Ill.

SPRINGFIELD -- The Illinois race for an open Senate seat might be the biggest political battle of 2010, at least when it comes to bragging rights.

This is the seat held by Barack Obama before he moved to the White House. It would be a major victory for Republicans to take the president's old seat out of the Democratic column in a state that, on paper, is strongly Democratic.

To pull off that coup, Republican leaders are backing Mark Kirk, a commander in the Naval Reserve and five-term congressman with moderate views on issues like gun control and abortion.

Kirk outrages some conservative activists, who consider him a traitor to fundamental GOP principles, but that hasn't translated into support for any of his rivals in the primary. One group canceled a debate because it couldn't find evidence that any of Kirk's opponents reached even 5 percent in opinion polls.

There's more competition in the Democratic primary race, and more vulnerabilities.