When Senator Bernie Sanders dropped out of the presidential race in early April, he vowed that the progressive movement he championed would carry on. And while at nearly every turn, he has encouraged his supporters to unite behind Joseph R. Biden Jr., the Democratic nominee, he and others in the party’s left wing have tried to nudge the former vice president more toward the policy goals his movement supports.
In recent days, he has been sounding more direct notes of caution to the Biden campaign, urging in public and in private that the former vice president, a centrist, must do more to excite progressive voters. He has emphasized, in particular, that Mr. Biden should work harder to appeal to young voters and Latinos; both are groups that overwhelmingly supported Mr. Sanders in the primary but Mr. Biden has so far struggled to connect with as the nominee.
“Senator Sanders is confident that Joe Biden is in a very strong position to win this election, but nevertheless feels there are areas the campaign can continue to improve upon,’‘ Faiz Shakir, Mr. Sanders’s former campaign manager, said in a statement on Saturday, which was first reported by The Washington Post. “He has been in direct contact with the Biden team and has urged them to put more emphasis on how they will raise wages, create millions of good paying jobs, lower the cost of prescription drugs and expand health care coverage.”
“He also thinks that a stronger outreach to young people, the Latino community and the progressive movement will be of real help to the campaign,’‘ Mr. Shakir added.
Mr. Sanders has put pressure on the Biden campaign publicly, too.
“Biden’s views are not mine, my program was much more progressive, But he has a strong program,” Mr. Sanders in an interview on Friday with PBS, “And I think he’s got to do a better job in getting it out, to be honest with you.”
Asked during the interview how confident he was that Mr. Biden would defeat President Trump, Mr. Sanders responded that he thought there was “a strong chance” that the former vice president would win but also counseled against complacency.
“Am I here to tell you absolutely, this is a slam dunk, no chance that he will lose? That is not what I’m saying,” Mr. Sanders said.
“You got to give people an alternative or reason to vote for you other than saying, ‘I’m not Donald Trump,’” Mr. Sanders added. “And that means speaking about an economic program, which Biden has. It is not as strong as I would like it. It is not the Bernie Sanders program.”
Echoing one of his most prominent surrogates, the filmmaker Michael Moore, who warned late last month that enthusiasm for Mr. Trump was “off the charts,” Mr. Sanders said in the interview that Democrats “should be nervous” about Michigan, Pennsylvania and Wisconsin, all battleground states that Mr. Trump won in 2016.
“What we have got to do is gin up the enthusiasm by talking about what Biden will do for working families in America and do a better job in exposing to the working class of this country the degree to which Donald Trump has sold them out and in fact is a fraud,” Mr. Sanders said.
The pressure from the left reflects the delicate line the Biden campaign faces as it tries to keep enthusiasm high among progressives while fending off charges from Mr. Trump that Democrats are dominated by socialists and extremists out of touch with voters, particularly in pivotal states like Michigan, Wisconsin and Pennsylvania.
Others in the liberal wing of the Democratic Party have also been pressing Mr. Biden to adopt more progressive measures and have expressed frustration at times that the policies he has offered do not go far enough on issues including health care, climate change and the economy.
A joint task force with the Biden camp on key Democratic issues produced a series of recommendations that frustrated some progressives because they largely reflected ideas that were already broadly popular among liberals. And there was palpable outrage that one of their most prominent new leaders, Representative Alexandria Ocasio-Cortez of New York, only received a 60-second speaking slot at the convention, which some progressives perceived as a slight.
Still, progressives have publicly been united in their desire to oust Mr. Trump, rallying around Mr. Biden and shying away from any denunciations of his stances. Mr. Sanders’s speech during the Democratic convention last month was a particularly powerful call to action for them to join the rest of the Democratic Party in ousting Mr. Trump. And he has held multiple virtual events in support of Mr. Biden, including a speech two weeks ago on the economy even as he has made clear that he and Mr. Biden have different views and different policy agendas.
“I would hope that, while people will have strong disagreements with Biden — I do — for the moment, put that aside,” Mr. Sanders said in the PBS interview on Friday. “That’s what, in a sense, coalition politics is about: You come together for a common goal. The goal is to defeat Trump.”