"An executive order in the United States is a directive issued by the President, the head of the executive branch of the federal government. In other countries, similar edicts may be known as decrees, or orders-in-council. Executive orders may also be issued at the state level by a state's Governor. U.S. Presidents have issued executive orders since 1789, usually to help direct the operation of executive officers. Some orders do have the force of law when made in pursuance of certain Acts of Congress, when those acts give the President discretionary powers."
From wiki. He can do it. But is taking a chance. So far all amnesty has hurt any President who gives into it. And people are sick of being promised tighter borders if we just give amnesty one more time.