LAS VEGAS — Joe Biden took aim at Bernie Sanders’s votes on gun legislation earlier in his congressional career, calling them “immoral,” in some of the harshest rhetoric the former vice president has used on the campaign trail against 2020 Democratic rivals.

“It’s just flat-out immoral, it’s just flat-out immoral,” Biden said Thursday at a closed-door meeting with members of the anti-gun group Moms Demand Action. “You know, committed Republicans and some Democrats, like Bernie Sanders voted five times, five times against background checks and waiting periods notwithstanding the fact that millions of people were denied having access to weapons of destruction because they didn’t qualify.”