U.S. Rep. Bill Foster, a Naperville Democrat, says he'll take a good look at running for Senate in 2016 in a possible challenge to U.S. Sen. Mark Kirk.
"I am seriously considering running for the United States Senate because I believe that voters deserve the strongest possible alternative to Senator Kirk," Foster said in a statement.
Kirk, a Highland Park Republican, has left little doubt about his interest in a second term. He held a large fundraiser Monday that included Gov. Bruce Rauner and other top Illinois Republicans.
"If you're looking at running against him, that's the take away -- the depth and scope of Kirk's support," former Illinois House Republican Leader Tom Cross told The Associated Press.
Foster is serving his second term in the current 11th Congressional District and was first sent to Washington in 2008 in a special election to replace former House Speaker Dennis Hastert.
Foster joins U.S. Rep. Tammy Duckworth of Hoffman Estates as suburban Democratic lawmakers eyeing a 2016 bid. Reps. Cheri Bustos of East Moline and Robin Kelly of Chicago are also said to be weighing a run.
Kirk brings to the race a statewide victory none of the would-be Democratic candidates can boast of. He continues to recover from a 2012 stroke, and at his fundraiser joked about how his wheelchair use would affect a campaign.
"The walk across Illinois got junked," Kirk said.
Radio host and former congressman Joe Walsh has said he's considering a primary election challenge to Kirk.
Foster is the U.S. House's only physicist and has sought to play up that background. In announcing he's considering a Senate run, Foster criticized Kirk for signing a letter to Iranian leaders about nuclear talks.
"Just recently, with his signature on the incredibly irresponsible letter to the government of Iran, we've seen Senator Kirk put his own politics ahead of the interests of our state and our country," Foster said.
Kirk has sponsored legislation trying to stiffen sanctions against the country.
Republicans took aim at Foster immediately.
"Millionaire Foster seems oblivious to his destructive record, but his votes for higher taxes and burdensome regulations have hurt Illinois families," Andrea Bozek, a spokeswoman for the National Republican Senatorial Committee, said.
•The Associated Press contributed to this story.