Think about it: Biden and Clinton share the same bases of support -- establishment Democrats, the labor movement, the environmental community, minority voters -- except that Clinton has a lot more of that support. And they, largely, hold the same -- or very similar -- views on the major issues of the day.
This chart, documenting the polling averages of Clinton, Biden and Bernie Sanders, shows the largely zero-sum game the vice president and the secretary of state are playing.
Given that, and the fact that Biden and Clinton are totally known by Democratic primary voters, the only way that Biden goes up -- in any meaningful way -- is if Clinton goes down. It's simple. There aren't enough "establishment" voters for Clinton to stay in the 50s in polling AND for Biden to win.
How do you pull voters off of a candidate who is both well-known and well-liked by a primary electorate? You try to make that candidate much less well liked.
For Biden, that would almost certainly mean turning the race into a choice between an authentic (if at times impolitic) politician in the vice president and a forever-triangulating and calculating one in Clinton. For Biden, that case is best made by going after Clinton on her private e-mail server -- which Bernie Sanders, amazingly, gave her a total pass on during the first Democratic presidential debate last week. You cast the decision to set up the server at all -- and then to take months and months before apologizing for it -- as the politics of the past, reminding people of the things they don't want to be reminded of about the time the Clintons last ruled Washington.
The question is whether Biden has the stomach for that sort of personal attack against Clinton. Politicians, as a general rule, tend to shy away from going harshly negative -- insisting (wrongly) that their best chance to win is by making the positive case for their candidacy and not talking bad about the people they are running against. But elections are about choices. The only way you win if you are not the best-liked or best-financed or poll-leading candidate is to create a stark (and favorable) contrast between yourself and the person who is those things.
Biden could choose to simply focus his candidacy on the time he spent by President Obama's side and his experience in the Senate. But such a bid would amount to a sort of victory lap -- like when Yankees closer Mariano Rivera went to every ballpark in his last year before retirement and they gave him all sorts of gifts. It's nice, it warms the heart and it ensures Biden will never seriously challenge Clinton for the nomination.
Beyond just whether Biden will run, then, is the question of how he will run. You (and he) might not like it, but his best -- and really, only -- option is to go after Clinton as aggressively as possible in hopes of disqualifying her in the eyes of lots of Democrats who support her now.
Politics ain't beanbag, after all.