Transition to one-party-system

[HisGrace]

Outside of some hyper conformist countries in East Asia you're not going to get a single party state without one side "cheating". Either through an outright far right coup or the Democrats creating a technocratic "soft despotism" state where all dissent is scrubbed from the internet and media, as many on the left seem interested in doing these days.

[HisGrace]

No more than any other western country usually being dominated more by one side than the other.

Germany has been run by a single party for the past 15 years.

Not the same thing since Germany is a parliamentary system. In the US you have to control both the WH and Congress, with congressional elections happening every two years. There are many more opportunities to lose power.