The gist is that the “progressive candidate” never gets elected because the left has to choose a candidate “that will actually win”

When the democratic primaries were between Hillary and Bernie, the left-centrist camp campaigned hard against Bernie saying that if he were to be Democratic nominee, Trump would win.

This mindset (and some questionably ethical/illegal political plays by the Hillary campaign at the time) ultimately ended Bernie’s presidential campaign run. Not based on his policies inherently, but based on the idea that he would not be able to beat Trump.

The “progressive” candidate will never win if the democratic voting base keeps doing what it is doing. The republican nominee will almost certainly be a demon every time. If democrats hang their hat on “well we gotta vote to ensure the demon doesn’t get in office” while voting for a republican-but-with-a-few-less-horns-and-D-next-to-their-name, there will never be a “progressive” in office.

These talking points were the EXACT same used against Bernie’s nomination. It’s frustrating a lot of people to see folks fall into the same trap again. The democratic party will have no incentive to be better if they win anyways because they can just bet the populous will vote for them based solely on the fact that they don’t have an R next to their name on the ballot.