Paul G. Kirk, a Longtime Kennedy Ally, Chosen as Kennedy's Interim Successor

Paul Kirk is expected to get the immediate attention of top Democrats in Washington looking for all the troops they can find for the upcoming battle over legislation to overhaul the nation's health care system.

But the new junior senator from Massachusetts might not necessarily be the deciding vote on health care because some moderate Democrats are also wary of the developing legislation. Democratic leaders are trying to reach the 60-vote threshold, the magic number needed to end floor debate and stymie a Republican filibuster.

Massachusetts Gov. Deval Patrick on Thursday named former Democratic Party Chairman Paul Kirk Jr. to fill the Senate seat held by Edward Kennedy until a Jan. 19 special election.

Kirk, a former aide and longtime Kennedy friend, will give President Obama the critical 60th U.S. Senate vote he needs to pass a health care overhaul this year.