Joe Biden didn't fail to weather the plagiarism storm because of the moral compunctions of his party. He failed to weather it because he lacked the standing to be a bankable candidate. Let me demonstrate.Amybear and I saw "Delaware, what state is that in?" on a T-shirt at Hot Topic a few weeks ago. What I said still holds true, Biden is senior senator from a 3 electoral vote state that the Democrats would win anyway. A candidate from someplace larger in the midwest or the south would be a much better choice.
I live in Delaware. When I visit My Girl in North Carolina, people hear me talk, notice my accent (or lack thereof), and ask where I'm from. I tell them that I live in Delaware. They ask what state thats in. This isn't a criticism of the geographic knowledge of North Carolineans. Delawareans get this a lot no matter where we go in the US.
Delaware is a small state with 3 counties and, more importantly for a national political race, 3 electoral votes. We're not exactly New York, California, or Texas. This isn't the place to raise up a major national figure.
McQ is noting that Biden tests as liberal according to all the major political organizations. That is probably true, but I would wager most Democrats test liberal because of party line politics. On the flip side, most Republicans will be arch-conservatives. The truth is that among Democrats, Biden and the rest of the Democratic Leadership Council are regarded as a pretty conservative group. To the party faithful he looks like a moderate, so he probably won't fare well in the primaries. To the party unfaithful, he looks liberal so he won't fair well in the general elections. That isn't exactly the best of both worlds.