Rep. Mark Kirk (R-Ill.), who has reportedly gone back and forth in deciding whether or not to run for Senate, was spotted by RCP walking into the weekly Senate Republican luncheon early this afternoon. He was clearly in foreign territory -- on the Senate side of the Capitol -- as he and an aide had to ask someone where the room was.

As he walked into the luncheon room, Kirk was welcomed by Louisiana Sen. David Vitter and former Federal Reserve Chairman Alan Greenspan.

"It's good to be here," RCP overheard Kirk saying, before RCP was shooed away from the door by Capitol Police.

Illinois GOP Chairman Andy McKenna, who has been considering a run for the Senate as well, said last night that he would step aside should Kirk decide to run.

Kirk has faced competitive challenges in recent years in his 10th district. Kirk won the last two elections in the swing district with just 53% of the vote against Democrat Dan Seals. In 2008, President Obama won the district with 61 percent.