Joe Biden may come under pressure to decide whether he will challenge Hillary Clinton for the White House sooner than anticipated, as liberal anxiety has prompted multiplying grassroots supporters to wonder if the vice-president might be knocked from his perch of studied neutrality and into a presidential bid.

A third-party political action committee urging Biden to challenge Clinton from the left in the smoldering controversy over her email arrangements has ballooned tenfold in the past week alone, the Guardian has learned, even as advisers close to the vice-president insist that he will wait and see about a 2016 run they say he is still “seriously considering”.



Hints that the Democratic search for alternatives to Clinton may be more heartfelt than previously thought – an earnest progressive case for an Al Gore candidacy emerged last week, and the email controversy has created air pockets in Clinton’s popularity ahead of her expected run – has some eyes wandering anew in the direction of the current White House.

Now, with Republican candidates launching formal campaigns and the Clinton machine not far behind, Biden supporters are for the first time displaying organizational structure: a Draft Biden web site last week that has gone from a list of 2,000 supporters to 20,000 backers nationwide, director Will Pierce told the Guardian.

What’s more, Pierce said, they are getting help from old Biden hands.

“Since we started this, a lot of people from Biden’s past, from when he was a United States senator as well as when he ran for president, have been coming out and supporting it and getting involved,” said Pierce, who said he has worked on political campaigns for about 10 years. “We’ve been feeding from their firehose, just because it’s been a lot of support.”

Biden has said for months that he will wait until summer before deciding whether to jump into what would be a battle against Clinton for the Democratic nomination for president. In January, Biden told ABC News that “there’s a chance” he would run. “I don’t think you have to make up your mind until the summer,” he said. “I think this is wide open on both sides.”

But from the vice-president’s perspective, the question has not changed, said Ted Kaufman, who was chief of staff for Biden for two decades in the Senate and was appointed to succeed him as senator after Biden’s elevation to the vice-presidency.

“His situation is the same as he talked about at the end of last year, that he was going to decide this summer,” Kaufman told the Guardian on Tuesday. “The main criterion is, what would he bring to the race, in terms of the ideas he cares most about.”

“Nothing’s really changed, the last four-five months, in terms of his position on running.”

Biden supporters point to his four decades in the Senate, where he served as chairman of the foreign relations committee and helped craft the Violence Against Women Act. Detractors point to his two previous unsuccessful presidential campaigns, including a 2008 effort that ended with a fifth-place finish in the caucuses in Iowa, which traditionally hosts the first voting in the presidential nominating contests.



Pierce, a former member of the US army reserves who deployed to Iraq and Afghanistan, said he supported Biden for his foreign policy experience. “A lot of people say this is an anti-Hillary Pac. It’s not,” Pierce said. “This is a pro-Joe Pac. We’re focused on the vice-president.”



They are not the only ones, said Dick Harpootlian, a former Democratic party chairman in South Carolina and vocal Biden backer.



“Behind the scenes, I continue to hear from folks who know I’m a Biden partisan that they’re anxious for him to get in the race, and anxious for him to do something overt,” Harpootlian said. “However, we all recognize he’s got a day job, unlike the rest of these folks, unlike Hillary Clinton.”



One well-connected Democrat in Iowa, where Biden popped up last month to talk economic policy, told the Guardian that the vice-president has “maintained he is still seriously considering” running for the White House, but “his time frame was a little longer than some people may be comfortable with”.



As the Democrat explained, if Biden sees Clinton faltering, “he may decide to pull the trigger”. However, Biden “doesn’t have to, he just wants to wait if he sees a moment”.



Clinton’s popularity among Democrats fell 15 points, according to a Reuters/Ipsos poll earlier this month, following revelations that she had used a private email account for official work as secretary of state. Clinton has been accused of using the account to hide her correspondence from the public eye. She has denied wrongdoing.



Even ahead of an expected launch of her campaign next month, most polls show Clinton as a clear frontrunner, including when she is placed head-to-head against Democratic primary candidates who might serve as the left’s answer to demand for a progressive alternative to her candidacy.



Topping that list of potential candidates has been Elizabeth Warren, the senator from Massachusetts, who has explicitly rejected the efforts of progressives to coax her into the race, under the banner of “Run, Liz, run!”. Clinton leads Warren 60-12 in an average of polling of a hypothetical primary matchup – numbers that would be reflective of the widespread perception that Clinton is running and Warren is not.



Biden fares slightly better when matched up against Clinton: a PPP poll this week of likely Democratic voters in Florida saw Clinton leading by 58-14. The gap is typical of other polling in other states, at this early stage – even as the Texas senator Ted Cruz kicked off the official campaign season ahead of expected declarations from a deep bench of Republicans in April, including Kentucky senator Rand Paul and Florida senator Marco Rubio.



Other potential Democratic primary candidates with less name recognition than the sitting vice-president, such as Maryland’s Governor Martin O’Malley or former Virginia senator Jim Webb, have yet to establish themselves as national figures.



Kaufman, the longtime aide, rejected the notion that Biden’s decision was tied to the fortunes of a Clinton campaign. The former secretary of state and first lady is expected to announce a presidential bid as early as next month.



“He and Hillary Clinton are good friends,” Kaufman said. “And ‘friend’ is used a lot in Washington loosely – very loosely. But he and Hillary have been friends for a long time.”