‘We’re holding a gun to our own heads,’ said Sen. John Cornyn in June. He was talking about President Trump’s threat to impose tariffs in order to force Mexico to crack down on illegal immigration into the Unites States. Many congressmen agreed, fearing, as establishment figures are prone to do, that Trump was risking the whole economy for some nebulous border demand.

A month later, it seems Trump’s tariff gambit has worked. After Mexican officials agreed to crack down on illegal immigration to avoid US-imposed tariffs, the Department of Homeland Security reports that border apprehensions dropped from 144,278 in May to 104,344 in June — a 28 percent decrease.

Some have attributed the drop to warmer weather, not the 20,000 Mexican National Guardsmen sent to the country’s borders with the US and Guatemala. It couldn’t possibly be that Trump’s plan worked, surely not.

Celia Muñoz, President Obama’s former Domestic Policy Council director, said, ‘It is very hard to pin fluctuations in the numbers month by month to any particular factor,’ adding ‘We believe it has more to do with temperature in the desert than anything.’ The Wall Street Journal notes ‘Border Patrol arrests of people crossing the border illegally tend to fall in June, as temperatures rise and the journey for migrants becomes more difficult.’

A closer look at migration patterns discounts the weather explanation. Although encounters between CBP and migrants tend to decrease in the summer, no decline comes close to this year’s 28 percent drop.

When looking at the total number of migrants, this month’s decrease is abnormally large. Between October 2013 and this month’s report, the recent drop in immigration is the largest decrease over a single month at 39,934. The next closest drop occurred between January and February 2017, when apprehensions dropped by 18,832 during the first two months of Trump’s presidency.

These numbers correspond with Mexico’s renewed efforts against illegal immigration. In June, Mexican authorities apprehended 29,153 migrants, up from 23,679 in May, and a recent low of 6,637 in December.

The Mexican government has a strong incentive to keep these numbers up: according to the enforcement agreement, the Trump administration expects Mexico to accept asylum requests if the migrant flows to the US do not decline significantly. As Mexican officials work to limit the flow of migrants and hold more asylum seekers awaiting adjudication in the US, the volume of border apprehensions could continue to drop from May’s 13-year high.

Once again, it seems, Trump’s tariff threats have been called crazy, only to then pay off.