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Republican Donald Trump has called for a ban on Muslims coming into the U.S., saying, "Our country cannot be the victim of tremendous attacks by people who believe only in jihad."

Senator Ted Cruz has warned, "Our enemies are not tired of killing us. And they're getting stronger," while Senator Marco Rubio cautioned, "What happened in Paris could happen here. These are radical terrorists who want to kill us."

Democratic candidate Hillary Clinton has warned of retaliation from Trump's comments — quote — "He is becoming ISIS' best recruiter. They are going to people showing videos of Donald Trump insulting Islam."

For our discussion on this, we're joined now by Stephen Walt, professor of international affairs at Harvard University, and Beverly Gage. She's a professor of 20th century American history at Yale University.

And we welcome you both.

Beverly Gage, to you first.

How long have candidates used fear in one form or another in American politics? And how successful has it been?