Daniel Gross has a great essay in the current Newsweek. The headline is "Dems Are the New Republicans." The gist of it is that, this time around, the establishment candidate is a Democrat, Hillary Clinton. So-called Wall Street Republicans are frustrated with the Bush administration's incompetence and fiscal irresponsibility. The business elite traditionally has been fiscally conservative but socially moderate. As the Republican Party has become more and more extreme in its social policies, as well as spendthrift, it has alienated that key part of its base. Right now it matters because those individuals are big donors, but they represent a lot of votes too.
Unfortunately, the Democrats face the same risk. As they move to fill the vacuum left by the Republicans, they move further and further away from what it is fair to call their Socialist wing. Conceivably, a leftist splinter third party candidacy could have the same effect Nader's had in 2000. Working against that scenario is the fact that the 2000 election came at the end of an eight year Democratic administration. Now the electorate is suffering from Bush fatigue, so a leftist third party candidacy seems unlikely to get much traction.
And although Hillary Clinton grew up as a Goldwater Republican in Park Ridge, Illinois (which is known locally as Park Rigid), it seems hard to imagine that a Hillary administration won't be Democratic in most traditional senses. Having grown up a Goldwater Republican myself, I'm not too worried.