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 that 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, Mrs. 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.
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 pro-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’s respect and esteem.”
On a recent stop at a diner in Laconia, N.H., Mrs. Clinton answered a voter’s question about why she had supported bankruptcy legislation that Senator Elizabeth Warren, Democrat of Massachusetts, and other liberal activists opposed. Unprompted, she raised the vice president’s role in the bill.
“I said, ‘It’s really important to me that we don’t hurt women and children, so I will support it even though there are other things I don’t like in it,’ ” Mrs. Clinton told the questioner, Jo Smith. Then she added, “It was Vice President Biden who was the senator from Delaware and the Republican co-sponsor that I was talking with.”
Aides to Mr. Biden did not comment. And Clinton aides, speaking on the condition of anonymity because they did not want to be identified discussing strategy in public, said that the effort to mobilize Democrats behind her was a natural progression of her candidacy, and unrelated to any potential challenger.
But several Democrats who have been in close contact with the campaign say they see a new sense of seriousness among her advisers about the prospect of a Biden candidacy. Mrs. Clinton’s team has been adamant that they are not behind efforts to draw negative attention to Mr. Biden, or to do anything to pressure him.
Among the clearest signs in the last week was a series of phone calls from Mrs. Clinton and two of her top advisers, Huma Abedin and John Podesta, to the financier Robert Wolf, a major Democratic donor who is now supporting Mrs. Clinton but who recently met privately with Mr. Biden. In an email, Mr. Wolf confirmed recent discussions with Mrs. Clinton and her aides.
Mrs. Clinton raised roughly $28 million during the last three months, her campaign said on Wednesday — a sharp drop from the $47.5 million raised in the previous three months, partly because of the sluggish summer fund-raising months and the possibility that Mr. Biden will enter the race.
Mr. Biden’s allies have made clear they are watching Mrs. Clinton’s poll numbers and the fallout over her use of a private email account at the State Department. And it has become increasingly clear that the activity by Mr. Biden’s associates to prepare for a potential campaign and to assess the amount of money and staff available to him has gained the attention of Mrs. Clinton’s operation.
The specter of Mr. Biden looms as a potential danger, but also as an incentive to motivate Mrs. Clinton and her operation, and to recover the fighting form she developed late in the 2008 presidential primary.
“I think they’re trying to create the impression that it will be difficult for anybody to climb up and beat Hillary in the superdelegate count,” said Ed Rendell, a former governor of Pennsylvania who is supporting Mrs. Clinton. But, he added, “I wouldn’t pressure people too hard if I were them.”
Much of the Clinton campaign’s focus has been on the so-called superdelegates, the elected officials and party elders who have significant influence in the nomination process, and whose endorsement carries weight with party insiders. Some superdelegates who have withheld their endorsement of Mrs. Clinton, in part because they are waiting to see if Mr. Biden will enter the race, have experienced heightened pressure from the Clinton campaign.
Should he decide to run, Mr. Biden and Mrs. Clinton would compete aggressively for the backing of African-Americans, who have a hugely favorable opinion of Mrs. Clinton but who remain fiercely loyal to President Obama, and could see Mr. Biden’s candidacy as a continuation and affirmation of the first black president’s legacy.
Mrs. Clinton has made it a priority to reach out to African-Americans throughout her campaign, with sweeping speeches on criminal justice reform and voting rights. James H. Hodges, a former governor of South Carolina who has endorsed Mrs. Clinton, said he liked and respected Mr. Biden — a line Clinton supporters often recite by heart — but concluded, “There is only one person who could beat Hillary Clinton in our state, and that’s Barack Obama, and last time I checked, he’s not eligible to run again.”