Bernie Sanders’ first major tangle with Joe Biden — over a 2010 deal that Biden struck with Republicans that liberals believed threatened Social Security — helped fuel his national rise.

Now Sanders is set to reprise that clash Tuesday night on the debate stage, where the Vermont senator is preparing to lay into Biden over his record on Social Security.

For the past week, Sanders and his campaign have telegraphed his attack over the former vice president’s long-standing record entertaining cuts to the program that are anathema to progressives and many mainstream Democrats.

Sanders’ speechwriter and senior adviser David Sirota said Tuesday will be time for Biden to answer hard questions about his past onstage.

“Joe Biden has repeatedly worked to cut Social Security, and has never offered up a good explanation for that crusade. His Social Security record is not only atrocious on a policy level, it is an enormous political vulnerability in both a primary and a general election,” Sirota said. “Bernie Sanders has exactly the opposite record — he’s fought those cuts and fought to expand Social Security, and that is a contrast Democratic voters deserve to know.”

Biden’s campaign, which has been reluctant to hit back, has responded so far by pointing out his current plan calls for expanding Social Security. And they point to Sanders’ past praise of Biden as a retort.

Biden’s advisers said the former vice president will be ready to take on Sanders and prevail against his attacks onstage just as he did when opponents Kamala Harris, Kirsten Gillibrand, Julián Castro, and Bill de Blasio went after him, only to see their critiques fall flat as they lost ground and exited the race as Biden pressed ahead.

Sanders, though, differs from those other candidates in one important way: He has a devoted base of loyal followers who show no signs of deserting him, many of whom want to see Sanders take the fight to a rival they view as the embodiment of the Democratic establishment by focusing on one of the party’s signature legacy programs, Social Security. He has also already repeatedly criticized Biden for his votes for the Iraq War and free-trade deals on the debate stage without seemingly suffering.

The Sanders team’s expected assault comes as he is at the top of the polls in the first-in-the-nation caucus state of Iowa, but still significantly polling behind Biden among seniors. It’s not guaranteed he will execute the attack on Biden in a sustained way: After previous debates, some of his aides and supporters have been disappointed that he hasn’t confronted Biden more aggressively.

The two men’s history over the issue provides a window into their political personas, pitting Sanders, the left-wing outsider against Biden, the moderate dealmaker with a legacy of working with Republicans. Already, that positioning that has proved politically challenging for Biden in the leftward-shifting Democratic primary.

In proposing a Social Security plan during the primary with none of the cuts or changes he once countenanced, Biden has moved more toward Sanders — a triumph for a progressive movement that fought for years to ensure Democratic politicians would only consider growing the program, instead of raising age eligibility requirements or freezing cost-of-living adjustments to make it pay out less.

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