Right. This isn't a sprint, it's a marathon. One of the most frustrating things I've seen progressives do is not get everything they want and then rage quit politics without realizing that this is even worse than only getting some of what you want.
In one respect, I wish progressives could be more like Republicans. After Roe v Wade, Republicans didn't rage quit politics. They pushed for abortion bans, lost, tried again, lost, and repeated until they got some small concession. Then they used that to slowly, over 50 years, build until they overturned Roe.
Now, obviously, I disagree with their goals. However, I can admire the long term effort put into this. If progressives could do this (with much better goals, of course), we might be able to do some amazing things. Yes, it would be slow at first and that can be frustrating, but imagine if we could have a country 30-50 years from now as far to the left as the Republicans are to the right (but much more sane).
Or just go one step further and have all Congressional members of the opposing party killed.
Biden would never do this and I don't want him to, but let's suppose that Trump's "legal theory" is correct and Biden wakes up tomorrow thinking that he's sick of dealing with the Republicans' malarkey. He orders some military groups known to be loyal to him to round up every Republican member of Congress along with certain Supreme Court justices. They are all executed. Then Trump is brought in and executed as well.
Now what would happen? Would Biden be charged with mass murder? No, he's immune to prosecution. You need to impeach and convict him first. But nobody remains who would impeach him. So he's totally immune as he appoints left leaning Supreme Court justices and expands his "early Republican retirement program" to right leaning Federal judges.
Again, I wouldn't want him doing this, but according to Trump this would be totally legal.