Hillary Rodham Clinton, the 2016 Democratic front-runner, with Joseph R. Biden Jr. in 2013.

By AMY CHOZICK and MAGGIE HABERMAN

September 30, 2015

Hillary Rodham Clinton’s campaign, increasingly worried about the threat of a challenge from Vice President Joseph R. Biden Jr., is making a sudden and urgent effort to throw roadblocks into his path.
After months of voicing doubt about a challenge from the vice president, Clinton campaign operatives are viewing Mr. Biden’s entry into the contest as a serious possibility and are trying to rally the party’s apparatus and its donors to her side. They have flooded uncommitted Democrats with emails, phone calls and a plea for them to sign a letter, a copy of which was obtained by The New York Times. In the letter, Democrats are asked to “pledge to support Hillary Rodham Clinton at the 2016 Democratic National Committee Convention with my unpledged delegate vote.”
A campaign aide said given the mistakes of Mrs. Clinton’s 2008 campaign, they had always planned to make an early and aggressive push to lock down superdelegate support.
This Saturday, hours before Mr. Biden appears as the keynote speaker at the annual gala of the Human Rights Campaign, the most influential gay and lesbian political group in the country, Hillary Clinton will have breakfast with the same group. And next Tuesday, former President Bill Clinton will appear on “The Late Show with Stephen Colbert,” after an emotionally powerful appearance by Mr. Biden that became a viral video among some in the Democratic Party.

Interactive Graphic | Who’s Winning the Presidential Campaign? History suggests that each party’s eventual nominee will emerge from 2015 in one of the top two or three positions, as measured by endorsements, fund-raising and polling.

Mr. Biden has kept even his loyal supporters guessing about whether he will become a candidate. But the Clinton campaign is not taking chances. A subtle critique is emerging from the campaign’s allies about the potential vulnerabilities Mr. Biden would bring to the race.
This week, David Brock, who created the Clinton group Correct the Record, which is coordinating with Mrs. Clinton’s campaign, told Chicago Magazine his “gut” told him Mr. Biden would not run because “he’ll realize that at this point in his career, he can go out with everyone& …Read More