Never underestimate the liberal ability to shoot themselves in the foot.
In 2000, disgruntled liberals who felt that Gore wasn’t progressive enough cast their votes for Ralph Nader, which ended up being the difference in a close election that handed the White House to Bush. Rather than be realists, and cast a vote that would count, they decided to vote for their narrow interests, despite not having a shot at winning. It was hubris, in my opinion — a common failing (and one that I’ve certainly fallen prey to, myself). In the end, we all paid the price of their principles.
Now, in 2008, we have a similar situation. Hillary supporters claim that there isn’t really any policy difference between her and Obama. I don’t believe this (given her war authorization votes, her introduction of an anti-flag-burning bill, her support of the Patriot Act, her views on the Unitary Executive, etc.), but let’s just say we’ll take that position as true. Fine — there’s no policy difference between the two.
Given that, why not vote for Obama over Clinton? If you’re getting the same policies, why cast your vote on a candidate who, according to recent polls draws 50/50 with the Republican front-runner in a general election, when the polls show Obama winning against the Republican candidate by a wide margin?
Why risk handing the election to the Republicans, when the policy differences are (supposedly) nonexistant?
It’s Nader all over again. Hillary supporters will throw away the general election, just to make a point.