ISIS goes after any group that deviates from its extreme ideology, dissident Muslims, for example, or the Yazidis who practice an ancient religion distinct from both Islam and Christianity.

The First Amendment to the Constitution says government can't establish a religion, but neither can it limit the exercise of religion. And that's the issue here. What does it mean to be free to exercise your religion? It's not about what you can believe. It's whether you can act on those beliefs.

Fidel Castro outlasted U.S. presidents determined to overthrow him, survived the collapse of the communist bloc that sustained him and outlived many of those who wanted to replace him. For those reasons, he will go down in history as among the world's most skillful politicians, even if his achievements largely die with him.

Hispanics are the fastest-growing evangelical group in the country right now, an important constituency. But Trump's views, especially his views on immigration, did not exactly go over well with this faith constituency. Rev. Rodriguez told me that Trump's invitation created something of a stir in his world.

There's a culture war in this country. Americans in recent years, as you know, have become more secular. They don't go to church as often. Bible reading, prayers in public are now frowned upon. And, of course, in addition to that, a lot of people have become much more supportive of LGBT rights. And in reaction to that, biblically conservative Americans feel that their faith is under assault.

When ISIS last year called for the destruction of the Yazidi people, President Obama said that would constitute genocide and he ordered U.S. forces to keep it from happening. Human rights advocates say Christians now face a similar threat Nina Shea directs the Center for Religious Freedom at the Hudson Institute.

The letter writers span the spectrum from left to right. Members say they don't want this to become a partisan political issue. In fact, there are reasons administration officials have been cautious in making a genocide declaration.