"The 2016 agenda was in many ways about consolidating and building on the achievements of the Obama administration and taking on some of the unfinished business of the Great Recession," said Jacob Leibenluft, an executive vice president of policy at the think tank Center for American Progress. "And what we see now is an attempt to do all that, but also considerably more, reflecting a greater consensus about what it takes to not only undo the damage that Trump has done, but really address the challenges that have existed in the country for several decades."
"The election of Donald Trump changed the perception of what was politically possible, and created new openings for ambitious ideas," added Leibenluft, who was a senior policy adviser on Clinton's 2016 campaign.
Biden has still faced plenty of criticism from the left for his policies. Shortly after beginning his campaign, he was forced to reverse his previous support for the so-called Hyde Amendment, which banned federal funding for abortions.
Progressive critics have also focused less on Biden's proposed plans for changes to the criminal justice system than his support for the 1994 crime bill, which they blame for creating a system of mass incarceration.
The debate within the Democratic primary has also focused on how candidates plan to pass their agenda through Congress. On this front, Biden has been more hesitant to embrace sweeping structural changes, such as eliminating the legislative filibuster in the Senate or adding seats to the Supreme Court.
"If you're not prepared to add seats to the Supreme Court, add Puerto Rico as a state, twist those arms, you're not going to get any of those climate policies because you're going to let Mitch McConnell determine your climate change policy," McElwee said.
Biden's message to voters doesn't always emphasize his agenda, either, choosing instead to promote his strength as a candidate against Trump or highlighting his close relationship with Obama. One of Biden's TV ads in Iowa for instance, highlights his plans to protect the Affordable Care Act while criticizing candidates who wish to replace it with a new system.
Warren and Sanders have each backed a plan that would replace the ACA with a single-payer system.
Biden's message heartens some center-left Democrats who fear the party will face consequences in the general election if it moves too far to the left.
"Our view on policy is that it serves as a kind of superstructure of the campaign and not the exterior," Bennett said. "The narrative and the message is what people react to."
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