Former Maryland Gov. Martin O'Malley at the Democratic debate Saturday night in Iowa said that net immigration from Mexico is zero.

During the conversation about immigration reform, O'Malley made his case for a comprehensive plan that would include a pathway to citizenship and said net immigration from Mexico is zero.

"Fact-check me," O'Malley said.

According to analyses conducted by the Pew Research Center, based on government data, the number of Mexican living in the U.S. illegally has declined over the last five years.

One of the Pew's reports from July said that in 2012, 5.9 million people were living in the U.S. illegally who were originally from Mexico, which was down 1 million from 2007.

In recent years, Pew said illegal immigration has leveled off and as a result, "net migration from Mexico likely reached zero in 2010, and since then more Mexicans have left the U.S. than have arrived."

Based on data from both the U.S. and Mexico, Pew said in a 2012 report that the net migration flow from Mexico to the U.S. had stopped and might have even reversed.

A study released in July from the University of New Hampshire, based on Census data, found that migration from Mexico to the U.S. has declined more than 50 percent in the last five years.

During the conversation over immigration, O'Malley called Donald Trump an "immigrant-bashing carnival barker," and added, "Our symbol is the Statue of Liberty. It is not a barb-wired fence."