U.S. Rep. Bill Foster (D-IL,11) has closed the door on a 2016 senatorial run.

Foster's decision against launching a bid to challenge U.S. Sen. Mark Kirk (R-IL) comes after U.S. Rep. Tammy Duckworth (D-IL,8) officially declared herself a Democratic candidate in the 2016 senate race late last month.

In a Friday statement, the congressman said he does not want to wade into an expensive and "ultimately unnecessary primary." Foster said he's backing Duckworth in her senatorial campaign and will assist in operating her finance committee.