You use the Tea Party as an example. Americans can't vote for the Tea Party. They have to vote for the Republicans.
In the US you vote for candidates, not parties. That's why you very often see people become senators, congressmen and even presidents who didn't have a long party afiiliation.
In Germany, political top positions are filled with people who have been a professional polititcian since their youth. Exceptions are very rare, I don't think it ever happened for the head of government (Kanzler). In Germany, you're serving a party, and are rewarded by the party with a paid position in the government once the party got elected. Apart from the "professionals", *all* top government functionaries are party affiliate, ie have a membership. That includes judges (county level upwards), state media, military (not sure actually), education and all sorts of other bureaucracts. These people don't have an ideology. They just know what's good for them.
Please don't quote constitutions or law to prove otherwise, these are irrelevant. It's the mentality, that counts, not the system.
In the US, there's a strong political polarisation that's reflected in congress. It might be much stronger than the reflection, but it is reflected.
In Germany, there is no such polarisation. CDU, SPD, FDP, the Greens are really the same ideology when compared to American diversity. There's "The Left" (yes, that's the name of a party) which is left of the rest, but not much. It's only real ideological difference is whether it's ok to have STASI functionaries in government offices, and they have a different opinion because so many of them have a history in the DDR. There's no point at all in voting.
I was raised there, I live there. It was the internet, google that enabled me to see the diversity of American thought. The gap between American pluralism and German conformism can hardly be exagerated.