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Congress often writes legislation to restrain executive officials to the performance of their duties, as laid out by the laws Congress passes. In INS v. Chadha (1983), the Supreme Court decided (a) The prescription for legislative action in Art. I, § 1—requiring all legislative powers to be vested in a Congress consisting of a Senate and a House of Representatives—and § 7—requiring every bill passed by the House and Senate, before becoming law, to be presented to the president, and, if he disapproves, to be repassed by two-thirds of the Senate and House—represents the Framers' decision that the legislative power of the Federal Government be exercised in accord with a single, finely wrought and exhaustively considered procedure. This procedure is an integral part of the constitutional design for the separation of powers. Further rulings clarified the case; even both Houses acting together cannot override Executive vetos without a 2⁄3 majority. Legislation may always prescribe regulations governing executive officers.

By what margin can congress over ride a Presidential veto?
two-thirds