I think a reading of Roman history shows the failure modes of a senate so often that I wonder if it was ever supposed to work more than a few hundred years.

Winner-takes-all democracies all suffer of the same issue.

There's a reason why every single democracy to turn authoritarian in the last 60 years has been presidential or semi-presidential.

The only parliamentary democracy to turn authoritarian since the 60s has been Sri Lanka, there's not a single other example.

I think you'll find America failed democracy.