Joe Biden has seized a clear advantage in the polls over President Trump, rallied a fractious party behind him and raised heaps of cash — trends that are giving liberals and left-leaning activists growing confidence that he will win.

But as they envision what Biden’s agenda as president would look like amid historic national crises, many are less optimistic. Some question his commitment to the transformational Franklin D. Roosevelt-style presidency he says he aspires to, pointing to a lack of specifics and an abundance of caution on certain policies. Others feel his intense focus on Trump will undercut his ability to build a political mandate for sweeping reforms.

“If I am to accept him as being a transformative leader, then I need to see evidence of his own transformation, and I haven’t,” said LaTosha Brown, the head of the civil rights group Black Voters Matter. Brown said she is unsure what a Biden presidency would look like beyond “Trump is gone.”

The concerns come as Biden’s “unity task forces,” which include liberal and moderate Democrats, issued policy recommendations on health care, immigration and climate change Wednesday. And Thursday, Biden will release long-awaited economic ideas, which will serve as a test of his commitment to the “revolutionary institutional changes” he says are necessary. Biden will deliver a speech Thursday in Pennsylvania on his plan to boost jobs and wages and “help America build back better,” according to his campaign.

Even as he has talked of more sweeping change, the presumptive Democratic nominee is running as a broadly acceptable alternative to Trump, refusing to adopt polarizing positions such as defunding the police or removing statues of the Founding Fathers that the activist wing of his party has championed. While he supports expanding the Affordable Care Act, he does not favor Medicare-for-all. And his plans to battle the novel coronavirus have stopped short of the ideas advanced by left-leaning members of Congress.

This posture has helped him build a lead over Trump in the polls and frustrated Republicans seeking to tag Democrats as extremists, but it has also stoked confusion about how he would govern.

Aiming to meet these concerns, Biden is aggressively building the foundation of a new government he would seek to install and is sketching a clearer picture of his earliest days in office. He is preparing policy rollouts and plotting his first legislative steps with advisers.

Beyond that, Biden aides are canvassing Democrats in Congress for ideas, according to aides and lawmakers; compiling a list of black women he could nominate to the Supreme Court and enlisting a close confidant to assemble a transition team.

But Biden’s pitch is missing some major details that activists want to see sooner. He vowed in early May to unveil the blueprint for economic recovery in “the coming weeks” and has promised to send Congress legislation on his first day in office to open a path to citizenship for undocumented immigrants. “I already have a bill written,” he said recently, but his campaign declined to provide further information or any draft text.

To some, Biden’s plans for his presidency often feel like secondary themes. At a pair of recent speeches in Pennsylvania and Delaware, Biden devoted much of his time to blistering attacks on Trump’s leadership. And in the video that launched his campaign, Biden focused sharply on the president, pointing to Trump’s comments that there were “very fine people” on both sides of a deadly white supremacist rally in Charlottesville.

“While it’s true that Trump is destroying himself, so it’s tempting to just let him do that, it is important to give hope to working families and be more specific about how government stimulus can put people back to work in sustainable ways,” said Larry Cohen, the chairman of Our Revolution, a liberal group aligned with Sen. Bernie Sanders (I-Vt.).

“I think it’s dangerous to set as the main protagonist of your campaign somebody other than yourself,” said Maurice Mitchell, the national director of the Working Families Party, a liberal organization.

Biden’s defenders note that he has presented policy proposals dating back to the primary, and that he has underlined his ideas a central part of his contrast with Trump. And Trump has plunged into historic levels of unpopularity for an incumbent, giving Biden an opening to run an effective campaign that taps into opposition to his rival.

“To the extent it’s a referendum on Donald Trump, Donald Trump has made it a referendum,” said Anita Dunn, a senior Biden adviser who accused the president of “disastrous leadership.”

She added, “What Joe Biden has done from the beginning of his campaign is lay out his vision for what America can be.”

In a welcome sign for the Biden campaign, Ady Barkan, a prominent liberal activist who has ALS and supported Sen. Elizabeth Warren (D-Mass.) in the primary, endorsed Biden on Wednesday. Barkan said on Twitter that Biden is “everything Trump is not,” and although “he & I have different perspectives on the world, winning this election is essential.”

Biden’s strategy is also an acknowledgment that even Democratic voters see this election as a referendum on Trump. Just 33 percent of Biden voters said they view their vote more as an expression of support for him, while 67 percent said they view it as a vote against Trump, according to a recent Pew Research Center poll. Seventy-six percent of voters supporting Trump said they view their ballot primarily as a vote for the president.

Many Democrats said the urgency of defeating Trump is the glue binding together a party with a history of internal warfare and messy disputes. If Trump is out of the picture come January, the old ideological disputes are expected to come roaring back, they said, further complicating the challenge Biden would face.

“Unquestionably, there will be dissension and disagreement because we are Democrats and that’s what we do,” said Sen. Richard Blumenthal (D-Conn.). “And it will be open and sometimes heated because again, that’s what we do. And Biden will, I think, accept the disagreement, because that’s who he is.”

Biden’s team is keenly aware of this challenge, which would only compound what would be an already daunting task: taking the reins of a country riven by divisions that deepened over the past four years and reeling from economic and public health emergencies as well as a difficult reckoning with racism and police brutality.

“Does it seem like there’s earlier planning than in previous cycles?” said Sen. Christopher A. Coons (D-Del.), a close Biden friend. “It feels like it’s more urgent to have answers to those questions, because there won’t be a period of relative calm and prosperity to say, ‘Well, let’s have some big discussions, let’s do a policy retreat.’ ”

The historic scope of the challenge has prompted Biden and his aides to begin mapping out the earliest days of his presidency, according to aides and allies.

Conversations about what to tackle first have focused heavily on the pandemic. Biden’s team “is kind of looking at January 20th of next year and anticipating that he will be facing, still, these three overlapping crises that have gripped the country this year,” said Jake Sullivan, one of Biden’s top policy advisers. “The first order of business will be, wherever we find ourselves in the trajectory of the pandemic come January, to get the virus under control.”

The exact response, Sullivan said, will depend on the situation, and could entail seeking to implement the proposals Biden has already put forward, such as free coronavirus testing and paid family leave for those affected. Biden may also consider expanding social safety-net programs and enhancing the production and distribution of vaccines and treatments.

In addition, Biden’s team is eying an economic relief package to assist families, small- business owners and state and local governments. “There’s the recovery side of this — the build back better side,” Sullivan said.

Among other ideas, Biden’s team is looking at how to invest in job creation, clean energy and infrastructure, as well as bringing back manufacturing to the United States to reduce dependence on other countries, Sullivan said. His team is also looking at ways to increase pay for caregivers and educators.

Biden alluded to these ideas on May 8 when he promised, “in the coming weeks, I’ll be laying out a detailed plan for the right kind of economic recovery.” He has not yet released a plan, though he is expected to provide more clarity in his Thursday speech.

A senior Biden campaign official attributed the lag to Biden’s desire to use his platform to focus attention on fighting racism and police violence in the wake of recent killings and holding Trump to account for the new spike in coronavirus cases.

Some supporters put little stock in comprehensive campaign proposals. “I do not think he should put forward a detailed plan at this point. It would be superficial and electoral,” Jeffrey Sachs, Columbia University economics professor, wrote in an email. “Serious plans take time and consultation across the country.”

Beyond combating the pandemic, Biden has vowed to sign executive orders “on day one” to restore Obama-era environmental rules nullified by Trump. He has said he will send Congress “a transformational plan for a clean energy revolution” within his first 100 days.

He has also released an immigration outline and a plan for black America, two areas where his response has drawn concern from activists.

Less clear is his strategy for expanding the Affordable Care Act with an optional public insurance program, a likely massive undertaking that could require immense political capital and months of negotiation. Campaign officials have said this is a priority but have not set a specific timetable.

The Biden camp has already begun to think about how to bring together the Democrats’ liberal and moderate wings. In May, the Biden and Sanders campaigns announced “unity task forces” to issue recommendations on health care, immigration and other topics. Those teams issued a 110-page report on Wednesday recommending that Biden and the party’s platform committee adopt specific positions on climate change, criminal justice reform, the economy, education, health care and immigration -- the latest signal of their collaboration.

The teams advised committing to eliminating carbon pollution from power plants by 2035 and reaching “net-zero greenhouse gas emissions for all new buildings by 2030.” The report also recommended supporting people at risk of lacking health insurance during the pandemic, with the government paying for costs to continue insurance for those who lost their jobs and the guarantee of a deductible-free health plan administered by the federal government until the coronavirus crisis ends. But the plan stops short of embracing longtime liberal aspirations such as a single-payer government health-care system.

“Though the end result is not what I or my supporters would have written alone, the task forces have created a good policy blueprint that will move this country in a much-needed progressive direction,” Sanders said in a statement.

Biden, who served in the Senate for 36 years and has close relationships with many lawmakers, has asked his team to engage members of Congress for policy ideas. Sullivan, policy director Stef Feldman and others have engaged in the talks, campaign officials said. Blumenthal recalled the campaign seeking his thoughts on “what we should be thinking about doing.”

House Democrats, led by Speaker Nancy Pelosi (D-Calif.), have passed scores of bills to overhaul police training, climate change, gun control and other topics that have gone nowhere in the Republican-controlled Senate, giving party leaders some ready-made blueprints for legislation next year. Biden is in regular touch with Pelosi and Senate Democratic Leader Charles E. Schumer (D-N.Y.), Sullivan said.

The Biden campaign has also begun to think about personnel. Biden said for the first time publicly last week that he is vetting a list of black women who he would potentially name to the Supreme Court if elected. The former vice president has also said he will have a diverse administration that will “look like America,” amid criticism that his campaign operation is too white.

Biden has tapped Ted Kaufman, a former chief of staff who succeeded him in the Senate, to start putting together a transition operation for the campaign. After the convention, the full transition effort will likely be announced, as is historically the norm, Dunn said.

“New presidents get a few big bites at the apple,” said Jared Bernstein, who served as chief economist to Biden when he was vice president and still advises him informally. “Putting things off is probably going to be the enemy of legislating them.”