Obama was chided by pro-immigrant critics as the “Deporter In Chief,” back in 2012, when Immigrations and Customs Enforcement removed record numbers of immigrants, mostly from Mexico. However, levels have dropped 42 percent from that all-time in the 2012 fiscal year  to the period between Oct. 1, 2014, and Sept. 28, 2015, the AP reports.

Why the drop? No one factor explains the reduction in deportations. Here are a few theories.

Felons, Not Families

In November of 2014, president Obama announced that the Department Of Homeland Security would be “focusing enforcement resources on actual threats to our security. Felons, not families.”

By one metric, the White House achieved that goal. Convicts make up a slightly higher percentage of deportees than they did one year ago, up to 59 percent from 56 percent according to data obtained by the AP .

Yet the drop in deportations hasn’t been matched with a corresponding uptick in criminal deportations. In fact, raw numbers of convict deportations are slightly down, according to the AP.

Central Americans Overtake Mexicans

The origins of incoming migrants has also changed, and that could have brought deportations down the Christian Science Monitor observes. Central American migrants outnumbered Mexicans for the first time in 2014.

An uptick in violence may be responsible for an exodus of migrants from countries like El Salvador. Many Central American migrants are resisting removal, petitioning for asylum and other forms of protection that would allow them to stay in the U.S. Some awaiting hearings are being released on bail, others with GPS bracelets and the rest are in immigration jails.

What does that mean for deportations? According to the CSM, deporting Central Americans is more costly, and takes more time. Instead of putting them on a bus, ICE has to put them on a plane.

The Economy, Estúpido

With high unemployment in the U.S., especially in the construction industry, many Mexican migrants are staying home and net migration from Mexico has hovered around zero since 2010 . A lack of economic incentives may be driving down illegal immigration from other countries as well.

An improved standard of living in Mexico has also contributed to a lower birthrate, meaning that there are less young people looking to risk a life in the U.S.

The Obama administration still oversaw far more deportations in the past year (around 232,000) than his predecessor George W. Bush (whose administration averaged 79,000 per year). But deportations are dropping, and the president might be able to escape his derisive nickname.