Rep. Mark Kirk (R-Ill.) has decided not to run for Senate -- a reversal from reports earlier this week that he was definitely jumping in. The news was first reported by the Washington Post.

Kirk's decision not to run comes on the heels of the leading Democratic candidate's opting out of the race. Attorney General Lisa Madigan announced Wednesday that she would instead run for re-election, leading to reports later that day that Kirk would run.

Left from the fallout is state GOP Chairman Alex McKenna, who had been considering running against Kirk, and two Democrats -- state Treasurer Alexi Giannoulias and businessman Chris Kennedy, son of the late Robert F. Kennedy. Giannoulias has raised $1.8 million so far after a dropoff in pace in the second quarter.