Well if they are going to pick a liberal Republican than that will happen. Ridiculous that this should even be considered. It is a shame that the Republicans have gone so far left that you can't tell a difference between Republicans and Democrats. You know if a liberal Republican (Rommney and Guiliani) ran against Nebraska Senator Nelson...who would be more conservative??? Probably Nelson. That is a sad commentary. (Yes I know that Nelson is not running, just an example of the disaster that the Republicans are making).
(Between you and me, I think I'm seeing why Republicans were shown the door last fall.)
But to get the Democratic nomination Nelson would have to act like a typical Democratic candidate or he'd split the party.
If Romney or Giuliani gets the Republican nomination, it will be because one of them has convinced other Republicans that he's in the party's mainstream. A party split is another possibility, but if that looks to be the likely result of nominating Giuliani or Romney, their candidacies will suffer in the primaries.