Sen. Mark Kirk (R-IL) took the oath of office Monday evening to be formally seated in the U.S. Senate where he will finish out the term vacated by President Barack Obama on his election to the White House.
Kirk, a former House member, was sworn in by Vice President Biden around 5:45 pm ET. Kirk's victory over Democrat Alexi Gianoullias reduced the Democrats to 58 seats, counting the two independents who caucus with them, versus 42 seats for the Republicans.
The lack of at least 60 Senate votes they can count on means Democrats on their own can't stop Republican delaying tactics like continued floor debate. They would need two Republicans to join them and that hasn't happened often.
It also increases the difficulties that would stem from defections by Democrats, particularly those facing difficult re-election bids in 2012.