Facing one of the most nail-biting choices since the presidential election, David Paterson, the New York governor, has been told he would be guilty of "political malpractice" if he named anyone other than Caroline Kennedy as the state's new junior representative in the Senate.

Mr Paterson, under intense pressure from some of the country's most powerful political dynasties as he ponders his decision, has sole discretion to appoint a replacement for Senator Hillary Rodham Clinton, who is moving to the state department in Barack Obama's administration.