Political parties are always concerned about electability, but much of this is speculative. I read in comments sections that the Republicans want Obama to win, because they know they can beat him - so vote Hillary. I have read people assert with equal vehemence the contrary notion, that the GOP would rather face Sen. Clinton in the general.
This is need for narrative and false belief in a controllable universe at work. People making these assertions usually seize upon one (or even two!) ideas and try to ride that all the way home. McCain will look old next to Obama...Hillary will carry the Latino vote in key states... Yawn. Very few people have the knowledge of what really does turn elections, those few will tell you it is chancey and complicated, and even they shy away from predicting this far out. The rest of you, you don't know.
One thing we can predict, however, is that if the Democrats lose in November, there will be enormous I-told-you-so's from one faction or the other, sure that their candidate would have beaten McCain, if only the others had listened.