I distinctly remember Democrats opposing Trump on moving the embassy to Jerusalem. They never fought him as much as they should, but they did fight him.

Exactly, so we can't rely on Democrats to effectively contain Trump as you suggested we might. They are not strong or reliable enough. They capitulate far too easily.

Let's not forget this is also what lead to the rise of the DSA and the largest protest movement in American history.

What really led to the DSA growing so much was Bernie Sanders radicalizing millions with his 2016 run. Then, the squad capitalized on that energy in 2018 and onwards, leading to many DSA members being elected nationwide, which then further grew the organization through the attention they bring.

I know it's not considered "cool" amongst leftists to admit electoralism can ever lead to positive outcomes, but them's the breaks. None of this would have happened if not for them.