Constitutional scholars are not needed. Clearly, in English, the President and Vice President of the United States hold civil offices under the United States and have previously taken an oath as officers of the United States.

The amendment specifically says "the United States"...TWICE. Clearly, the President and Vice President are officers, not "of any State" but of "the United States."

The amendment clearly applies to the President and Vice President. Perhaps they had President Andrew Johnson in mind.