Our country WAS founded with the separation of church and state in mind. Our founders did not want political leaders to abuse their power like the King of England and all the other monarchies in Europe did. Our founders set up our country so that anyone could believe in any religion they want or no religion. Trying to legislate Christianity into court rooms, school or other public places in just as bad as Iran, where Islam is the state government. Our country will end up a worse tyranny than Iran if we allow the separation of church and state to be sullied by stupid partisan politics.
That being said, you should be able to say whatever you want on your own about religion. Merry Christmas is fine. Christmas trees are fine. Buddhist temples are fine. Just pay for them yourself and display them on your own property.