What a week.  According to the Washington Post's Chris Cillizza -- who reported two days ago that Rep. Mark Kirk was moving forward with a 2010 Senate bid -- the North Shore Republican has now decided not to run.  The reason? 

[The announcement] followed a meeting of the Illinois Republican congressional delegation on Thursday in which his colleagues refused to back Kirk in a primary against Illinois Republican Party Chairman Andy McKenna due, in large part, to his vote in favor of President Barack Obama's climate change bill.

Kirk's move makes McKenna the almost certain Republican nominee against either state Treasurer Alexi Giannoulias or Merchandise Mart CEO Chris Kennedy next fall.

Apparently, Kirk just couldn't stand the thought of crossing John Shimkus and Don Manzullo.

UPDATE (3:35 pm): Or maybe not. Roll Call is now reporting that Kirk says he is still discussing the race with McKenna and that the Post report is "incorrect."  Cilizza has added this to his original post:

Although Kirk has already told several national Republicans today that he will not run for the Senate, there is an ongoing effort now to convince him to re-think that decision, according to several sources close to the discussions. Pressure is now being brought to bear on Andy McKenna, who, according to knowledgeable sources, had told Republicans insiders that he would not run if Kirk got into the race. Once Kirk signaled he was indeed running, however, McKenna reconsidered and made clear he would in fact stay in.