Lol packing the court is categorically different than assassinating them.
It's not "assassination", it's targeted killing, and it's perfectly legal and above board. The Supreme Court said so. The President gets to decide who dies and there's no judicial review possible because it's a "political question".
At minimum, what you're describing would lose a bunch of Democratic support, and if a bunch of your own party is against you it's ultimately not going to work.
Master statesman Saddam Hussein had a solution for that specific problem. You get all your party members in a room, demand they pledge personal loyalty to you, and then force the ones who did pledge to shoot the ones that didn't. Bam. Party discipline secured.
I'm not asking for much. Just for the president to exercise the same tactics to control uncooperative democratically elected governments at home that he uses abroad. Biden allegedly couldn't do anything because Manchin and/or Sistema just couldn't be brought to the table for some weird reason. Somehow the guy who controls the army, the intelligence aparatus, the justice department, the DEA, the IRS, and the Post couldn't find any way to make them move even a little teeny weensie bit.