The US has a lot of problems. For one thing, we have a Presidential system in which control of Congress can be held by a different party than the Presidency, which leads to a situation where there are two "plausibly legitimate" elected governments that are in conflict. In many other countries this has resulted in coups and instability (usually in favor of unilateral executive power.) The US is unique in that we're basically the only country that has thrived under this system. For what it's worth, the alternative is a Parliamentary system where the legislature elects the executive.

The US also has a lot of gerrymandering of Congressional districts, and far too few of them (don't get me started on the ridiculous Senate.) Plus it has lots of minority veto points like the filibuster requiring 60 votes, the electoral college, and the Supreme Court. Some of these exist "by design" and can be beneficial, but they also present the possibility of legitimacy concerns.