Take a look at our system - it needs work, but it's head and shoulders above the US.
A THREE plus party system, free healthcare that works almost perfectly (we live on average three years longer), a better education system by far (Canada is 3rd in math, science and reading, while the US is 14th), we have a lower crime rate, and a dramatically homicide rate (about four times lower), you can drink at 19, our air is cleaner on average, we use metric, we're bigger, and we've got routine.
Despite not having proportional representation or administrative-only cabinet (including PM), Canada's parliamentary system is a good model to follow. Semi-presidential can be done fairly easily. One - the president appoints an administrator in a non-cabinet position, so it does not require Senate approval. The administrator answers questions from Congress and works with the different secretaries. Two - president suggests that the administrator be made a cabinet position, giving Senate approval powers. Three - president leaves actual administration to administrator and cabinet.
America has problems that Canada simply doesn't face on the same scale. America has 9times the population of Canada. Let's agree that every policy and every law has a down side or unintended consequences I think that is fair to say. Now when you apply these policies on a small small the negative effects may be limited or not noticeable but on a much larger scale the problems become more prominent. This is why many of Canada's and smaller European policies would be difficult to implement in America despite those policies being effective there. In reality you can't just copy and paste policies from one country to another there are many factors.