Jeffords, 70, has been adamant in saying he will seek re-election, but there have been increasing concerns voiced about his health in recent weeks.

Jeffords was elected as a Republican to the U.S. House in 1974 and to the U.S. Senate in 1988, but he abandoned the party in 2001 because of disagreements with the Bush administration.

"In order to best represent my state of Vermont, my own conscience and principles that I have stood for my whole life, I will leave the Republican Party and become an independent," said Jeffords on May 24, 2001.

At the time the Senate was evenly divided and Jeffords' decision to become an independent and caucus with the Democrats put the Democrats in charge of the Senate.

Jeffords has maintained in the past two years that he would seek another term in the Senate: He has hired campaign staff and has more than $2 million in his campaign account.

But increasing questions about his health have dogged the senator even though his spokesman, Erik Smulson, said just over a week ago that "Sen. Jeffords is in excellent health, and he's looking forward to waging a spirited campaign."