Mr. Biden, 72 years old, lost two previous bids for the White House, in 1988 and 2008, and he would enter the 2016 contest as a clear underdog. Yet as a sitting vice president with loyal supporters in states that hold early contests, he has the potential to scramble the Democratic field.
A Wall Street Journal/NBC News poll earlier this month showed that Americans’ image of Mr. Biden is growing more positive. A total of 40% saw him in a favorable light, versus 31% who had a negative view of him. In November 2014, Mr. Biden’s favorability rating stood at 35%, compared with 38% who viewed him unfavorably.