Two important ways that the authors of the constitution limited the powers of the president is with separation of powers and checks and balances and a bicameral legislature. I believe that they did do a good job of balancing that power from what I've seen today, although there are loopholes. For example, the president is the commander-in-chief of the army, however only Congress can declare war. But the loophole to this is that the president can actually still wage a war as long as he doesn't "declare" it a war, he can still send troops abroad.