The vice president sums up his future decision with two qualifiers -- that no else runs who can do what he can, and that he still thinks he can deliver the goods.
Biden could decide that he is better qualified than Clinton on what he considers the key issues, but he would have to think twice if her already anticipated campaign has started strongly and generated initial momentum.
If he were to run and win in 2016, Biden would be 74 when he took office, making him the oldest ever to begin a presidency. By the end of his first term, he would be the oldest U.S. President in history.
So while he remains energetic and passionate, talking about getting his Corvette Z06 from zero to 60 in 3.4 seconds, the clock is ticking and Biden knows it.