When it became clear last month that former Vice President Joseph R. Biden Jr. would almost certainly win the Democratic nomination, many of the progressive Democrats who supported other presidential candidates were disappointed but not deterred. They quickly shifted their electoral focus to candidates lower on the ballot.

The plan was straightforward: They would donate to a slew of insurgent congressional candidates, and a stable of grass-roots groups would be ready and waiting to organize for the general election and beyond.

But that was in a pre-pandemic America, before the spread of the coronavirus caused thousands of deaths, about 10 million new unemployment claims in two weeks, and the halting of public events in the presidential race. Now many progressive candidates and the organizations that support them are struggling to adapt to a bleak reality — dried up fund-raising, unclear election dates, and a moratorium on tried-and-true political tactics like in-person phone banks and door-to-door canvassing.

“It’s an immediate effect on how we can plan, how we can grow, and even our month-to-month cash flow,” said Amanda Litman, the executive director of Run for Something, one of the many Democratic organizations founded after President Trump’s 2016 victory. “It’s really scary, because the candidates need more support than ever. And political fund-raising right now is plummeting, as is the rest of the economy.”

Ms. Litman said her group had already been forced to cancel fund-raising that was expected to bring in nearly $500,000. The coronavirus, she said, has made basic operational questions — including Run for Something’s survival through the November general election — a more open question.

There are also political challenges, said Waleed Shahid, a spokesman for Justice Democrats. Insurgent candidates are more likely to rely on door-to-door canvassing and rallies to show enthusiasm, activities that are functionally discontinued until further notice. Progressive candidates also tend to rely exclusively on small-dollar donations, which have experienced a downturn as people tighten their budgets.

“Incumbents have certain advantages in a crisis, namely access to the media as a voice of authority,” Mr. Shahid said.

The grim picture may have a profound political impact for the general election and beyond. Democrats were poised to have an organizing juggernaut ready for the 2020 election, with the goal of both reaching new voters and helping reverse the state and local losses they experienced during President Barack Obama’s years in power. Even more, liberal groups hoped this election cycle would formalize their political infrastructure, so the activism that erupted in response to Mr. Trump’s election could be harnessed going forward.

That may still happen, but it will require creative financial and digital solutions, according to interviews with several leaders of progressive political organizations and left-wing candidates running for office in states like New York and Ohio. Optimists have called it a time for political innovation, while others worry the structural barriers could stymie the progressive movement at a critical crossroads.

The outcome is of particular importance because the two most liberal presidential candidates, Senators Bernie Sanders of Vermont and Elizabeth Warren of Massachusetts, were surpassed in the primary race by the more moderate Mr. Biden. Ms. Warren ended her presidential bid last month, and Mr. Sanders still says his campaign has a “narrow path” but is facing increased calls from allies to cede the nomination to Mr. Biden.

The left-wing Working Families Party had to recall waves of canvassers who were collecting signatures for congressional, state and local candidates endorsed by the group. It has also scrapped multiple in-person initiatives: a volunteer training program that was to begin imminently and a two-day organization-wide convention in Milwaukee that was scheduled for May.

On the campaign side, Ohio canceled its primary just one day before voters in the state’s Third Congressional District were set to vote in a Democratic primary between Morgan Harper, a community activist who had previous jobs at the Consumer Financial Protection Bureau and as a corporate lawyer, and Representative Joyce Beatty, an incumbent with a long history in state politics. The state has rescheduled its primary to April 28, but has also mandated that nearly all voters submit ballots by mail, a move Ms. Harper said might depress turnout and give an advantage to candidates with higher name recognition.

“People are very stressed about contracting an infectious disease that has the potential to kill you while also dealing with the disruption to financial life right now,” Ms. Harper said. “And in the midst of that, while experiencing extreme financial stress, we’re going to ask them to have the wherewithal to go to a website, request an application, print it out and mail it back in — just to get a ballot.”

Suraj Patel, one of several challengers running in New York’s 12th Congressional District against the incumbent Democrat, Representative Carolyn B. Maloney, contracted the coronavirus in March, forcing him into quarantine.

The situation disrupted his campaign schedule, though he has been trying to work from home. Mr. Patel said his small dollar fund-raising had dropped off by 80 percent by the end of March.

“No doubt fund-raising is way, way, way down,” Mr. Patel said. “And it’s difficult to even ask people to give when most of them are either furloughed or at home or uncertain of what’s going to happen.”

There have been some silver linings for progressive candidates. Ms. Harper and Mr. Patel have ramped up digital contact with voters and repurposed campaign tools to provide information about coronavirus safety.

Jamaal Bowman, a progressive who is mounting a campaign against the stalwart incumbent Representative Eliot L. Engel in New York’s 16th Congressional District, pivoted to an online-only operation in a matter of days, said his campaign manager, Luke Hayes.

“One of the things about having such a broad base of small donors is that while asking them for that recurring donation of 10 dollars a month, you cultivate a relationship with them,” Mr. Hayes said. “I think some incumbents, you know, they just expect kind of checks brought in just based on their stature.”

Just as in the business world, where new digital tools have exploded in use, fresh political technology is also helping to fill gaps. Outvote, a political start-up in Boston that allows users to send voting and other political information to people in their social networks, has seen a rise in interest from progressive campaigns and causes as the pandemic spreads. Some have begun using Outvote to disseminate information about how to guard against the virus, said Naseem Makiya, the company’s founder.

On Thursday, the Progressive Turnout Project, a political action committee that supports liberal candidates, announced a nearly $3 million investment in phone banking that aims to leverage up to 12 million calls from volunteers to lower-propensity Democratic voters before Election Day in November.

“The more impersonal the mode, the less effective you’re going to get,” said Alex Morgan, the group’s executive director. “So while it is great that a bunch of groups are hopping onto text messages and digital, that’s more distant than you and I having a conversation right now.”

But progressives are also hoping that their message of big ideas has a new resonance in this moment of crisis. In interviews, group leaders said they were confident the pandemic had strengthened their calls for systemic change by exposing cracks in the country’s economy and health care system.

Ms. Litman said Run for Something, even with looming financial questions, had seen interest from prospective local candidates hold steady throughout March. Rahna Epting, the executive director of the progressive group MoveOn, said its membership had grown by more than one million in March.

“What we’re seeing is that the energy that normally we would funnel into physical protests and physical action, the energy is there and it’s growing exponentially,” she said.

On Sunday, the Working Families Party held its first digital rally, with appearances from the Rev. William J. Barber II and Stacey Abrams, who ran unsuccessfully for governor of Georgia in 2018 and now leads the voting rights group Fair Fight Action. Working Families plans to hold its May convention remotely.

“You know, it took me some time to get my parents FaceTiming with me in a way that made sense,” said Maurice Mitchell, the national director of Working Families. “And I think that’s happening on a broader level where people have different fluency with different types of technology. We’re all kind of learning together.”