After WW2 France seemed ungovernable. After fiddling with various things, the French re-tooled their form of government (and some other things, too), and things got vastly better.
In the 1980s Israel seemed ungovernable. We fiddled with various things, re-tooled our electoral system, the result was even worse than before, we went back to the original system - and things got better. Or rather, they got lots worse on other fronts (the 2nd Intifada started, for example) but it turned out the old-new system was working fine.
Sometimes changing the system fixes things. Sometimes not. It depends what the original problem had been.
The Economist discusses the political system in America, and wonders if it needs fixing or perhaps not.