How borders are drawn and enforced has far-reaching consequences, whether we live on either side of them or halfway across the world.

Even before president Trump’s tweet announcing his intent to sign an executive order to “suspend immigration,” immigrants were leaving the US. The US’s foreign-born population shrank 1.9% in March 2020, according to data from the US Census Bureau. It was the largest one-month decline since June 2001.

The US foreign-born population is now at a level similar to 2017, right after Trump signed an executive order banning immigration from a number of Muslim-majority countries.

The president has used the crisis to spread anti-China sentiment. His latest tweet “serves to distract from the main coronavirus response, demotivates front line healthcare workers or those researching a cure, many of whom are immigrants,” according to Xiao Wang, the cofounder of Boundless Immigration, a company that provides information and legal services to immigrants in the US.

A series of travel restrictions led to the slowdown. The global outbreak of Covid-19 prompted the US to restrict travel to and from China on Feb. 2 and expand the restrictions to Iran on Feb. 29. On March 13, restrictions were added for 26 European countries, followed by Canada and Mexico a week later. Many foreign nationals studying or working in the US found ways to return home before borders closed. Seasonal workers abroad—who are facing visa delays, high travel costs, and little to no US health insurance coverage—did not enter the country as planned.

Central American and Asian immigrant communities had the largest one-month drops.

It’s not just the US. In the trading hub of Guangzhou, China’s the third-largest city, the city mayor said at a briefing that there were only 30,768 foreigners left in the city. That’s down from a population of over 86,000 in December 2019.

Many countries stopped processing visas on arrival and suspended visa-free entry for certain people. Some immigrants, expats, and migrant workers chose to return home, if the situation permits.

The global immigration slowdown is temporary, but how governments react to it could have a lasting effect. Germany has arranged inbound flights for seasonal farm workers from Eastern Europe. Portugal granted temporary citizenship rights to immigrants and asylum seekers so that they could get access to the nation’s healthcare system.

Correction: Due to a calculation error, an earlier version of this item overstated the one-month decline in the US immigrant population.