Reply #33: Its in the Establishment Clause in the First Amendment [View All]

[OregonDem]

Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof....

By making a permanent religious symbol to be public property the state is creating a law which respects an established (or organized) religion, namely Christianity.
While it is true that this amendment says that Congress is the only one who cannot do it, later amendments (the 14th I think) to the Constitution stated that local and state governments had to abide by the Bill of Rights also. The president also swore an oath to uphold the Constitution which he is violating by doing this.
Although the Constitution doesn't specifically say "seperation of church and state" it is just easier to say than "Congress shall make no law respecting an establishment of religion".