One thing that can't be argued with: whoever David Paterson picks to replace Hillary Clinton in the Senate will need win an election at the end of Clinton's term in 2010, and again in 2012.
The impending campaign in an expensive media market has been cited as a reason to pick, say, Caroline Kennedy, who has the connections and the fund-raising capacity to do it.
It's also been cited as a reason someone like Kennedy might not want the seat–the Times wondered if she would be interested in the "unglamorous aspects of campaigning across New York’s 62 counties."
While electability is certainly a factor, history indicates Paterson might not want to base his decision on it.
A review of election results shows that in New York, no sitting Democratic senator has lost an election since at least 1920.
Courtesy of a reader:
1928:
Copeland (D, elected 1922) – Houghton (R) 49-481932
Wagner (D, elected 1926) – Medalie (R) 56-391934
Copeland (D) – Cluett (R) 55-371938
Wagner (D) – O'Brian (R) 55-451940
Mead (D, elected special election 1938) – Barton (R) 53-471944
Wagner (D) – Curran (R) 53-571950
Lehman (D, elected special election 1949) – Hanley (R) 50-451982
Moynihan (D, elected 1976) – Sullivan (R) 65-341988
Moynihan (D) – McMillan (R) 67-321994
Moynihan (D) – (R) Castro 55-422004
Schumer (D, elected 1998) – (R) Mills 71-252006
Clinton (D, elected 2000) – (R) Spencer 67-31