Setting aside the debate about whether anything "radical" can be achieved through electoral politics, I'd say Bernie was the harbinger of this. He didn't even set out to run a serious campaign in 2016, but people were so fed up with mainstream Democrats that they threw tons of energy and votes at him anyway because he was actually a "legitimate" candidate (a sitting senator, running on an issue tons of people cared about, in a Democratic primary instead of a near-hopeless third party bid). In 2020, when he ran a serious campaign from the start (and when people had another four years to radicalize), he had more success than any U.S. candidate who'd ever embraced the word "socialism" (including Debs). It wasn't enough to overcome the trifecta of Democratic ratfucking, poor luck with the timing of major campaign events, and an incredibly popular Republican opponent, but there was a pronounced upward trajectory. You can see that trajectory elsewhere, too, in the victories of additional DSA-backed candidates, progressive prosecutors, and explicit socialists like India Walton.

People will support the "radical" option if it has a chance. What they won't do is get so wound up in radicalism that they spike the football when there's nothing left to gain (e.g., after a leftist candidate loses a primary). Most will turn out for a backup option before not voting at all.