When Mr. Trump has made various claims about a decline in illegal border crossings in the past, he has tended to selectively choose points of time that showed the most drastic drops. His claim on Wednesday about a 40 percent decline was no different.

Border crossings did decline by 26 percent from the 2016 fiscal year to the 2017 fiscal year, and by 43 percent from the 2016 calendar year to the 2017 calendar year. Those figures, however, do not represent the current state of border crossings.

The New York Times reported last week that Mr. Trump had berated Kirstjen Nielsen, the homeland security secretary, for what he saw as a failure to adequately protect the border.

Sources: Customs and Border Protection, The New York Times