"When it comes to whom voters like among Barack Obama's possible running mates," according to Rasmussen Reports, "it's all about the also-rans."

Both Hillary Clinton and John Edwards, according to the latest numbers, strike a thin line between love and hate when it comes to voters: Both have very high favorable and unfavorable ratings. As for the other potential candidates?

The high number of "not sure" responses in the new survey indicates that voters are not even aware of many of the Democratic vice presidential possibilities. Sixty-one percent (61%), for example, are not sure how they feel about Kansas Governor Kathleen Sebelius, who is often mentioned as a dark horse candidate for vice president. Fifty-one percent (51%) say the same about Senator Jim Webb of Virginia, a Vietnam War Marine veteran who is highly regarded by many in the party, but Webb already has said he is not interested in being Obama's running mate. By contrast, only 2% say they are not sure what they think about Clinton.

As it turns out, being unknown might not be so bad in the VP stakes, especially among the prediction markets:

In the Rasmussen Reports vice presidential markets at the time of this survey, Bayh is favored by 33.9%, with Kaine at 18.2%, Biden at 15% and Sebelius at 13.3%. Clinton is near the bottom at 3.9%.

And the least favored of all? He's that millionaire populist from North Carolina. "No one," the report adds, "is trading in Edwards." Hmm...wonder why?