How can it produce tyranny?
Well, let's say that when the president gets elected, there were only two viable candidates. The system allows this to happen. People feel there are only two viable candidates so they don't bother voting for anyone else. And when they do vote, often they're voting AGAINST someone, rather than for their preferred candidate.
Then you have the Supreme Court, justices appointed by the president with the Senate's hand.
Then you have the Senate, which is probably the part of government that actually is elected as it was supposed to. However in the modern era this leads to an imbalance based on whether you have more of the smaller states at your disposal.
Then you have the gerrymandered House.
All in all the third party in the US has had zero presidents, has zero members of the House or the Senate, zero Supreme Court justices, zero governors of states, zero members of state upper houses, one member of state lower houses, and only another 182 elected officials in the whole country.
I could do the figures for you, showing just how undemocratic this all is, but I suppose you know already.
This has led to a system of government which is easily controlled.
Imagine for a minute that you're a billionaire who just wants to control the future of the country. Well, it's open for the taking. The Supreme Court ruled that spending money on politics is free speech. Wow. Allows you to spend whatever you like wherever you like. As long as you hide where the money comes from, people don't even realize you're doing it.
You can easily control Congress. Why? Because you make sure people know money is important. One Senate seat election, in PA I think, cost MORE than the whole of Germany's federal elections. Money buys success and you can direct your money easily because there are only two political parties to control.
You have a Senate seat, you only need to fund on candidate because there are only two candidates who are viable. In Germany this wouldn't be possible, as you'd have to target the whole country. Not just small areas and with so little opposition too.
Leads to politicians who are there for the money. Lick the rich man's ass and gold will come pouring out. All you have to be is the sort of guy whose principles are money, money and maybe some loose women, and you're the "perfect candidate" and you will receive a lot of money.