Power of the purse to stop him…..
Check it out:

The Constitution is unambiguous about which branch of the federal government has the authority to make laws governing immigration and control all money spent from the Treasury. It is Congress.

Article 1, Section 8, Clause 4 gives Congress the power to “establish an uniform Rule of Naturalization.”

Article 1, Section 9, Clause 7 says: “No Money shall be drawn from the Treasury, but in Consequence of Appropriations made by Law.”