To date, he has yet to win a primary and hasn't run since 1988. Speaking of 1988, Michael Dukakis was the first Greek-American to run for President, and he too fell upon hard times, losing to then Vice President George Bush. The only exception to the rule has been John F. Kennedy. As the first Catholic President, Kennedy did an arguably good job, but such success has not been duplicated since his election in 1960. Whether Joseph Lieberman will be an exception or succumb to the rule will be seen.
People are tired of negativity.
Al Gore's known for being a tough and negative campaigner. During the Democratic primary, Gore showed both as he attacked Bill Bradley on his record and integrity. Soon, Bradley fell by the wayside, and now Gore can and has let loose on George W. Bush. This time the negative campaigning doesn't seem to work. Bush has, by and large, run a more positive campaign with few ventures into negativity.