Senator Al, you are assuming that Kerry was a rational choice.
He was "rational" and electable to the ideologues who vote in the Democratic Party. Incredibly, to them, he was pretty moderate.
In reality (outside the lefty cacoon) America didn't see him as so electable. or moderate enough.
Nominating a Warner is a much bigger leap than nominating a Kerry in the very liberal Democratic Party. The two are vastly different on many issues.
Umm, liberals already disagree with Kerry on perhaps half of the issues.