Much has been made in the media about the Ukrainian government, if there is such a thing, 'invoking' the Budapest Memorandum as if it were a real military treaty. As I've pointed out much in the comments, this is false. It is not a treaty, has no effect of law that binds the United States to anything. It is merely a statement of diplomatic policy that continues at the whim of the consensus of the leaders that are party to it.
But if you want to see what a real, absolutely legal, ratified by the Senate, clear as day military alliance treaty really looks like, look no further than Lithuania:
Linas Linkevicius, Lithuania's foreign minister, responded on Saturday by invoking Article 4 of the North Atlantic Treaty, whereby NATO member states consult one another if their territorial integrity or political independence is threatened, for only the fourth time in the alliance's history (Ukraine is not a NATO member).Poland and Latvia have done so as well, as is their right under the North Atlantic Treaty.
So far, there are no indications that NATO allies are at risk from attack by Russia. But should such a thing happen, as hysterical commentary alleges, the United States is duty bound by the Constitution to defend its NATO allies.
NATO ARTICLE 5:
The Parties agree that an armed attack against one or more of them in Europe or North America shall be considered an attack against them all and consequently they agree that, if such an armed attack occurs, each of them, in exercise of the right of individual or collective self-defence recognised by Article 51 of the Charter of the United Nations, will assist the Party or Parties so attacked by taking forthwith, individually and in concert with the other Parties, such action as it deems necessary, including the use of armed force, to restore and maintain the security of the North Atlantic area.US CONSTITUTION ARTICLE 6 (Supremacy Clause):
This Constitution, and the Laws of the United States which shall be made in Pursuance thereof; and all Treaties made, or which shall be made, under the Authority of the United States, shall be the supreme Law of the Land; and the Judges in every State shall be bound thereby, any Thing in the Constitution or Laws of any State to the Contrary notwithstanding.US CONSTITUTION ARTICLE 2, SECTION 2:
He (the President) shall have Power, by and with the Advice and Consent of the Senate, to make Treaties, provided two thirds of the Senators present concur;NORTH ATLANTIC TREATY RATIFICATION BY THE SENATE:
The Senate gave its advice and consent to the North Atlantic Treaty on July 21, 1949, by a vote of 82-13.The only way this country is going to be automatically at war with anybody is if we or our treaty allies are attacked or face an imminent, immediate danger to our or their security.
None of these facts apply to Ukraine, which is not a NATO member and has no legal military alliance or defense pact with the United States of any kind. The Budapest Memorandum carries nothing even close to the language that you see above with respect to a real defense treaty. Therefore, the United States is not obligated to defend Ukraine by any reading of American Law.