I was talking to a friend some time ago about American politics, political parties, etc. During this conversation, I thought of something:

• If a single party controlled both the house and senate, they could always pass a joint resolution
• If the president also belonged to said party, the bills would never get vetoed
• The president couldn't be impeached, since the house and senate are under control of the party
• Because of this, the party could make the supreme court judges "disappear" and appoint new ones. Despite suspicions, he/she couldn't be impeached
• The party can then pass any laws they like, pardon anyone they want (meaning they can do anything illegal and get away with it), and even pass constitutional amendments to extend their reign without the supreme court stopping them.

I'm absolutely certain I've overlooked something that would make this impossible, and people have said so, yet never been able to find a reason. Is this possible, and if not, what stops it from happening?