Larry Downing/Reuters
Fearing a run by Vice President Joe Biden, Democratic presidential frontrunner Hillary Clinton is asking the party's donors and undecided delegates to sign a letter pledging allegiance to her campaign. The letter, which the New York Times obtained on Wednesday, asks Democrats to "pledge to support Hillary Rodham Clinton at the 2016 Democratic National Convention with my unpledged delegate vote." Efforts to mobilize Democrats behind Clinton have grown on increasing concerns of Biden's candidacy and in the wake of the controversy surrounding her use of private email while at the State Department. According to a recent Wall Street Journal/NBC News poll, Biden would outperform Clinton in the general election in hypothetical match-ups with top Republican presidential hopefuls.