The Debt Ceiling and Perry v United States

“The power given Congress to borrow money on the credit of the United States is unqualified and vital to the Government, and the binding quality of the promise of the United States is of the essence of the credit pledged...The Fourteenth Amendment, in its fourth section, explicitly declares: “The validity of the public debt of the United States, authorized by law, . . . shall not be questioned.” While this provision was undoubtedly inspired by the desire to put beyond question the obligations of the government issued during the Civil War, its language indicates a broader connotation. We regard it as confirmatory of a fundamental principle which applies as well to the government bonds in question, and to others duly authorized by the Congress, as to those issued before the Amendment was adopted.”

 - Perry v. United States, 294 U.S. 330 (1935)

The President has no power to borrow money on the credit of the United States under the Constitution, including the Fourteenth Amendment.