How does a system of checks and balances prevent any of the three branches from becoming too powerful?
The other responders provided the text book mechanisms by which checks and balances work. To some extent, they do actually work. However, in practice things aren’t so nice and tidy. Two general situations comes to mind: 1. Some of the branches may fail (or decide not) to restrain another branch. Many people are saying this about the current executive. Congress has watched Bush’s administration drastically increase the power of the presidency. 2. The branches may collaborate to mutually increase their power. Indeed, #1 above may fall into this category. If they all want power, they may get more of it not by holding the other branches back but by making consessions to each other in which everyone accrues power. I think that in practice, #2 happens the most.
