On health care, Clinton proposed offering a public insurance plan for Americans enrolled in the health care exchanges established by the Affordable Care Act. She also wanted to let adults older than 55 buy into Medicare.
Biden's plan goes much further: He wants to allow all Americans -- including those receiving insurance through their employer -- to buy into a government-backed insurance plan, a shift some progressives have said would represent an enormous change to Obamacare. (Biden also proposed significantly increasing the subsidies available to those who enroll in the public option.)
There's also a wide disparity between Biden and Clinton's climate change plans. Clinton proposed spending $60 billion on clean-energy fund as part of an attempt to make the U.S. 80% carbon-free by 2050; Biden wants to spend $1.7 trillion in federal money to make the country emit a net of zero carbon emissions by 2050.
"Joe Biden's climate plan -- I'm going to get canceled for this -- is quite ambitious," said Sean McElwee, co-founder of the liberal group Data for Progress.
Biden is also pushing to triple Title I funding for schools that educate low-income students, and to abolish the federal death penalty while encouraging states to do the same. Clinton wanted to preserve capital punishment in certain situations.
One of Biden's most prominent criminal justice reform proposals -- a $20 billion initiative that encourages states to reduce their prison populations in part by removing mandatory minimums for non-violent crimes -- also represents a new kind of plan from a major presidential candidate, according to Lauren-Brooke Eisen, acting director and senior fellow for the Justice Program at the Brennan Center for Justice.
"The candidates are all realizing they need to focus on ending mass incarceration, reducing racial disparities, ensuring more dollars are used on prevention and education than incarceration," Eisen said. "There's a wholesale recognition among leading Democratic candidates that incarceration has not made us safer; it ruins lives."
Liberal policy experts say Biden's robust agenda is a reflection of a Democratic Party that has shifted decisively to the left since Trump's election. Policies that would have been widely considered radical at the end of Barack Obama's presidency are now commonplace, forcing even veteran politicians like Biden to recalibrate.
But experts are also quick to add that they think Biden's agenda is also reflective of a recent shift in the policy community about the scope and severity of the problems facing both the U.S. and the world. On the environment, for example, they note that proposals naturally become more aggressive after the Intergovernmental Panel on Climate Change issued a new report in 2018 that warned the effects of a rapidly warming earth would be worse than expected.
In other cases, candidates are responding directly to proposals from the Trump administration that didn't exist when Clinton ran in 2016.