Each faith has a different view of God and prays in a different way. The Jewish God is one whose initial covenant with the Jewish people remains in place. The Christian God sees that old covenant as having been replaced by a new covenant in Jesus Christ, who they believe is God's son. The Islamic God, Allah, believes Jesus was a great prophet, but not God's son, and that Ishmael, not Isaac, is the child of Abraham whose line (the Muslims) God chose to bless.
Theologically this matters. Politically it shouldn't. It is of no concern to me if this president, or any president, issues prayer proclamations. I can pray, or not, without government encouragement.
Does it matter to God? Only if our prayers result in changed behavior. Should God be expected to bless a nation that tolerates, even promotes, so much evil?
Perhaps instead of a proclamation for a day of prayer, the president should consider reverting to Lincoln and the part of his proclamation that concerned "humiliation," repentance and a plea for forgiveness. According to Scripture, that is a prayer God always hears.