The First Amendment is misused by many on the left to suggest that any political position motivated by religion is somehow out of bounds in a country in which separation between church and state exists. But the separation of church and state isn't a separation between religion and state. If it were, the struggle against the slave trade, the Abolitionist movement, the Civil Rights movement of the 'Sixties, the campaign against child labor, and all manner of other social reforms universally acknowledged today to be good things but first advanced by Christians carrying their religious convictions into the public square would all have to be ruled out of bounds.
In fact, if the separation of church and state meant the separation of religion and state, the originator of the concept, Thomas Jefferson, would hardly have based his political theory as to the origin of human rights on the decree of "nature and nature's God!"
Sen. Rubio did an excellent job of making the point that it's conservative Christians, and not their often misinformed and frequently bigoted critics, who are the real advocates of religious freedom for everybody- including atheists.
If you haven't seen the video yet, here it is: