Well, not quite. The U.S. house currently has 220 Republicans, and to pass a bill takes 218 votes. If 3 Republicans decide they don't like something, the bill won't pass, and this is happening quite frequently right now. (The Democrats could decide to join the Republicans and pass it anyway, but so far this has not happened.)
The current President keeps wanting to pass bills which simply don't pass.
Likewise, the Senate realistically needs 60% votes to pass controversial legislation, and that just isn't happening either.
You're right that the U.S. congress used to vote far more upon regional lines or other non-party interests than it does now. There is something studied in political science (I can't remember its name) that predicts that well-funded, important elections will eventually converge on being 50/50, with the winner essentially being statistical noise.
You're right that defections haven't totally gone away, but I think the current Congress actually emphasizes how rare they are now. The only reason things aren't passing is because the house is so close that a tiny percentage of Republicans defecting can sink a bill. But the vast majority of Republicans follow the party line and basically none of the Democrats are willing to cross over either. In a system with realistic local representation you'd expect a lot more crossover in both directions.
This was the norm for most of the 20th century. Major legislation passed with votes from both parties - often over ⅔ and immune to a Presidential veto.
My reaction to this is to focus more on things locally.
I'm sure part of the issue is the move towards giant omnibus bills rather than bills addressing individual issues. They tend to emphasize the ideological differences between the parties.
The current President keeps wanting to pass bills which simply don't pass.
Likewise, the Senate realistically needs 60% votes to pass controversial legislation, and that just isn't happening either.
You're right that the U.S. congress used to vote far more upon regional lines or other non-party interests than it does now. There is something studied in political science (I can't remember its name) that predicts that well-funded, important elections will eventually converge on being 50/50, with the winner essentially being statistical noise.