Sen. Bernie Sanders announced on a livestream Monday that he's endorsing former Vice President Joe Biden, five days after suspending his own presidential campaign.

Why it matters: It's an effort to unify the Democratic Party behind the presumptive nominee after a divisive primary. "We have to make Trump a one-term president and we need you in the White House," Sanders told Biden.

The big picture: Sanders and Biden said they are forming task forces on health care, education, the economy, climate change, criminal justice and immigration — a sign of Biden's continued outreach to the progressive wing of the party.

"You've been the most powerful voice for a fair and more just America," Biden told Sanders. "You don't get enough credit, Bernie, for being the voice that forces us to take a hard look in the mirror."

Biden and Sanders asked each other a series of questions around some of these task force issues. Notably, Biden asked Sanders what policies could best help young people — a constituency that loves Sanders and one that he's been fighting for.

"I’m glad you are prepared to focus on that issue," Sanders told Biden. "It’s the right thing to do. If we believe in a strong democracy, which you do and I do ... [and] we understand in a competitive global economy we will need the most educated workforce in the world."

Between the lines: Now that Biden is nearly guaranteed the nomination, he will need Sanders' help in uniting the Democratic Party. That will be easier if progressives feel like they're getting something from Biden — policy concessions or personnel commitments for a potential Biden administration.

The task forces are a good start, but progressives will want something concrete — not just symbolic.

In 2016, Sanders and his movement fundamentally changed Democrats' policy discussion, bringing things like Medicare for All into the national conversation and changing some of the national party rules to be more transparent about the primary process.

Biden is unlikely to adopt Medicare for All, but the two have been talking for weeks and there are signs that Biden will meet Sanders in the middle on various issues.

What they're saying: "I know you are the kind of guy who is going to be inclusive," Sanders said to Biden.

"We are friends," Biden said. "I appreciate your friendship, and I promise you I will not let you down."

Go deeper: Biden and Sanders work toward truce on big issues