Montesquieu - The people of the US gives the government its power.
Montesquieu believed that the branches of government have no right to threaten the people, and that the people have the right over the government. To ensure that the government did not become too strong, he approved of the 'separation of powers', which is still seen today for the US in the three governmental branches: Legislative, Executive, and Judicial.
Voltaire - People are free to practice whatever religion they wish
Voltaire believed in the separation of the Church and State. To understand this, we must look back into history. Especially during the time of Galileo, the Catholic Church was also seen as a governmental head, as they were able to raise funds, set religious laws, and even raise armies (as seen in the Crusades). To ensure that the church did not become too powerful, Voltaire promoted the belief that the church and state should not be together, but separate.
Locke - The president has the power to veto a law passed by congress
The president has the power to veto, which makes sure that the Congress cannot be too powerful (Balance of Powers). This also ensure that Congress can think twice of their choices of passing the law (as they would have to vote again to allow it to pass.) The president can also suggest changes to the legislation. This can be clearly seen during the presidency of Abraham Lincoln, in which he made it more lenient for the Confederate states to rejoin the US, for example.
hope this helps
