National Day of Prayer

Here is the article that I was reading.  As I understand it the problem here is that Congress made a law establishing a national day of prayer which violates the first amendment.  I have read the constitution.  This particular day is observed by presidential proclamation.  
So the first question that pops into my mind is "what if the president issues the proclamation anyway?"  Seems like the only way to fix that would be through impeachment, but said impeachment would violate the first amendment's freedom of speech clause.  Then what do you do?  That would be fun to watch....from another country.
I noticed another day on the list that seems to violate the first amendment.  That would be Thanksgiving.  If you are giving thanks you are thanking someone.  Once Crabby up there in Wisconsin figures out who we are thanking and how we are doing it that will have to go.
Next we will have to cancel Christmas.  This one isn't a presidential proclamation.  It's a federal holiday, but it celebrates the birth of Jesus.  Can't have that can we.