President Trump signed an Executive Order on Wednesday calling for the construction of a border wall between the U.S. and Mexico, the first step toward delivering on one of the most controversial and oft-stated promises of his campaign.

He also signed a related order calling on the Department of Homeland Security to enforce existing U.S. immigration laws. That’s a rebuke to President Obama, who directed a controversial shift in policy by calling on enforcement agencies to focus on the most dangerous immigrants.