I must say, a poll released yesterday by Public Policy Polling shocked me.
PPP tested a race between Obama and Romney, along with seven independent candidates (one at a time).
Without a third candidate, Obama and Romney were tied at 45% each. The results with each of the independents included:
Michael Bloomberg: Romney and Obama both lose 3%, leaving them still tied.
Jon Huntsman: Romney loses 5%, and Obama gains 1%.
Ron Paul: Romney loses 12%, and Obama stays even.
Donald Trump: Romney loses 15%, and Obama gains 1%.
Sarah Palin: Romney loses 19%, and Obama gains 2%.
Ralph Nader: Romney loses 4%, and Obama stays even.
Bernie Sanders: Romney loses 4%, and Obama stays even.
Discussion below the jump.
The first thing to realize is that the poll was all given to the same people, so the differences aren't a margin-of-error thing. There are actual voters who become more likely to vote for Obama if Huntsman, Trump, or Palin join the race, and there are actual voters who would switch from Romney to Sanders.
So what does this mean?
Well, part of the reason that Romney loses votes to Sanders and Nader is probably that a lot of Romney voters don't know who Sanders or Nader are. (60% of John McCain voters are "not sure" whether they have a favorable or unfavorable opinion of Sanders, suggesting a lack of familiarity with the Socialist from Vermont.) But that means that an important chunk of Romney supporters would be holding their nose to vote for him.
Obama's support, on the other hand, is rock solid. He only has 45% of voters behind him, but that 45% can't be tempted by any sort of white knight, whether from the left or the center.
That's not to say that there aren't disaffected liberals out there. If Sanders, for instance, were to run, the President's support among people who describe themselves as "very liberal" drops from 86% to 81%. But he gains 1% both among those who describe themselves as "somewhat liberal" and "somewhat conservative." And because there are so many more people who are center-left or center-right than there are on the far left, he stays even overall.
But all of that is fine-tuning, a few percent here or there. While one can rightly question the base's enthusiasm for Obama, the poll suggests they won't desert him altogether in large numbers.
The Republicans, on the other hand, are ready to ditch Romney at the drop of a hat. Palin's entry into a three way race drops Romney's support among the "somewhat conservative" from 77% to 50%.
This changes my view of the 2012 race considerably. Of course, a lot could happen between now and the election. But as of this moment, President Obama does not appear to be vulnerable to a third candidate, while the Republicans appear deeply divided and dissatisfied with their candidates.