I am only familiar with Campaign Trail (pretty good for a free game), President Infinity (not realistic enough to justify buying it), and some emulator of a game that was made in 1992.
The Political Process is a good one if you have a windows computer and have Steam.
How does it compare to other games (such as Democracy 3) in terms of realism?
It's pretty realistic, sure there might be some outdated stuff due to averages of all senate/presidential elections combined to create an average. You can govern and all that as well.
Please explain what you mean by this.
You can't win as a Democrat in Texas or Georgia on the normal modes because of the fact that the Democrats did bad in Senate/Presidential elections until then and you can win as a Democrat in West Virginia, but I'm not sure if you could do it now and Iowa and Ohio is pretty close in elections because of that.