Hours after Sen. Edward Kennedy's (D-Mass.) passing from brain cancer at the age of 77, questions abound over who will succeed him, and how long that succession will take.

Massachusetts state law mandates that a special election be held to fill the vacant seat within 145 to 160 days of when the seat becomes vacant, placing the date of a potential special election between January 18, 2010 and February 2, 2010.

But with landmark healthcare legislation -- the trademark political issue of the late senator's lifetime -- in the balance in the Senate, Kennedy wrote Massachusetts lawmakers in recent weeks, urging them to reverse a 2004 law stripping the governor of the ability to appoint a nominee to succeed him quickly in the case of a vacancy.

"I therefore am writing to urge you to work together to amend the law through the normal legislative process to provide for a temporary gubernatorial appointment until the special election occurs," Kennedy wrote to Massachusetts lawmakers and top political officials in the state. Kennedy wanted the governor to be able to appoint a nominee, with the condition that any successor would give a personal commitment to not seek reelection in the following cycle.

The 2004 law was put in place by Democratic lawmakers in the statehouse in order to block then-Gov. Mitt Romney (R) from appointing a Republican successor to Sen. John KerryJohn KerryOne year ago today we declared ISIS atrocities as genocide Trump’s realism toward Iran is stabilizing force for Middle East 134 foreign policy experts condemn Trump travel ban MORE (D-Mass.), should Kerry have won the presidential election that year.

It's unclear whether or not state lawmakers could change the law after Kennedy's passing to allow Gov. Deval Patrick (D), a relatively unpopular incumbent, from appointing a senator.

Due to the long incumbencies of Kennedy and Kerry, the state of Massachusetts has not gone through a special election to fill a Senate vacancy since Kennedy himself was elected. Kennedy was elected in a November 1962 special election in a race to fill the vacancy left by his brother, President John F. Kennedy, who was elected president.

The current vacancy weighs on the prospects for healthcare legislation and a number of other legislative priorities for Democrats in the upper house. But some whip counts have long counted Kennedy -- along with another ailing Senate veteran, Robert Byrd (D-W.Va.) -- as unable to vote, leaving congressional Democrats short of the 60 votes needed to break a filibuster, but prepared for the prospect of lawmaking in Kennedy's absence.