U.S. Customs and Border Protection has used 2-chlorobenzylidene malononitrile, or CS, since 2010, and deployed it 26 times in fiscal 2012 and 27 times in 2013. The use dropped after that, but was still deployed three times in 2016, Mr. Obama’s final full year in office.

Use of CS rose again in fiscal 2017, which was split between Mr. Obama and Mr. Trump, and reached 29 deployments in fiscal 2018, which ended two months ago, according to CBP data seen by The Washington Times.

Border authorities also use another agent, pepper spray, frequently — including a decade-high record of 151 instances in 2013, also under Mr. Obama. Pepper spray, officially known as Pava Capsaicin, was used 43 times in fiscal year 2018, according to the CBP numbers.

The data poses a challenge to the current anger over the Border Patrol’s use of tear gas Sunday to prevent a mob from busting through sections of old border fence in California.