Biden is not really popular here at all in MA - and I'm talking about everyday Boston residents - but he's not unpopular because he's a liberal or because of his views on certain issues.
You ask people about him and they will tell you he's too old, or they'll just shrug... he just doesn't have that much enthusiasm here.
Up against the Republican, he's an automatic "Yes" vote - it becomes an ideological vote, but he would not survive a Democratic primary in the state of Massachusetts if there were a lot of other better candidates.
There's your problem.