Peter Bergen is CNN's national security analyst, a vice president at New America and a professor of practice at Arizona State University. He is the author of "United States of Jihad: Investigating America's Homegrown Terrorists." The opinions expressed in this commentary are his own. View more opinion articles at CNN.

(CNN) The Trump administration is framing the necessity of a southern border wall, in part, as a response to a national security emergency involving terrorists. This is a barrel of bunkum and balderdash served with generous helpings of hogwash.

Where to begin? Let's start with the fact that there is no terrorism emergency. 2018 saw one of the lowest yearly numbers of jihadist terrorism cases in the United States -- 14 -- since the 9/11 attacks, according to New America, a research institution that tracks terrorism.

The largest number of such cases was in 2015 when there were 80.

While the number of terrorism cases is not an exact proxy for levels of threat, it certainly says something about the scale of the threat and the United States has seen a steep decline in the number of jihadist terrorism cases over the past four years.

This decline tracks with the declining fortunes of ISIS. When it controlled territory the size of the United Kingdom, thousands of Islamist militants joined or attempted to join ISIS, including from the United States. Now the geographical caliphate is almost entirely gone and ISIS recruitment has slowed to a trickle.

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