WASHINGTON (AP) — In April, Bernie Sanders repeatedly stood shoulder to shoulder with President Joe Biden, promoting their joint accomplishments on health care and climate at formal White House events while eviscerating Donald Trump in a widely viewed campaign TikTok video.

Then just last week, Sanders was bluntly warning that the crisis in Gaza could be Biden’s “Vietnam” and invoking President Lyndon B. Johnson’s decision not to run for reelection as the nation was in an uproar over his support of that war.

Such is the political dichotomy of Bernie Sanders when it comes to Joe Biden. They are two octogenarians who share a bond that was forged through a hard-fought primary in 2020 and fortified through policy achievements over the last three years.

Now, in this election year, Sanders will be Biden’s most powerful emissary to progressives and younger voters — a task that will test the senator’s pull with the sectors of the Democratic Party most disillusioned with the president and his policies, especially on Gaza.