This is largely true. The US’s political left gained a ton of traction behind Bernie Sanders. As we know his campaign went nowhere (twice). There are a handful

This is largely true. The US’s political left gained a ton of traction behind Bernie Sanders. As we know his campaign went nowhere (twice). There are a handful of progressive candidates winning some primaries, but this is abysmal in the larger context. For every progressive that succeeds there is another progressive that fails (see e.g. Nina Turner in Ohio and Jessica Cisneros in Texas). And for every attempt there are 10 non-attempts. And we are even seeing equally many conservative democrats that honestly should belong in the Republican party in the national and state legislators. Outside of partisan politics the left is seeing some more successes, that is in the broader culture war. This includes broader acceptance of LGBTQ+ rights, calls for immigration reforms, calls for reprimands for centuries of slavery, etc. However these successes are not making their way to the legislator by a long shot, and quite often to the contrary (see e.g. reversal of Roe v. Wade). And I say this firmly from the left wing of the political spectrum.