This was most apparent during the 1868 impeachment trial of Andrew Johnson, in which members of Congress routinely characterized the president as a constitutional officer. “The electors may elect a president and vice president, but the Senate only can remove them,” Senator John Sherman of Ohio said during the trial. “The president and the Senate can appoint judges, but the Senate only can remove them. These are the constitutional officers, and their tenure and mode of removal are fixed by the Constitution.”
The authors of the brief also assemble evidence to show that the framers of the original Constitution of 1787 also considered the president an officer of the United States. An early version of the impeachment clause, for example, referred to “impeachments of any national officers.” The final version of the clause states that
Judgment in Cases of Impeachment shall not extend further than to removal from Office, and disqualification to hold and enjoy any Office of honor, Trust or Profit under the United States: but the Party convicted shall nevertheless be liable and subject to Indictment, Trial, Judgment and Punishment, according to Law.
The president is subject to impeachment, which means, by definition, that he holds an office under the United States and is an officer of the United States. The president is also covered by the foreign emoluments clause, which applies, again, to any “Person holding any Office of Profit or Trust” under the United States.
If this wasn’t enough, the authors of the brief surface a quote from Luther Martin, a delegate to the Philadelphia Convention, who explained during the impeachment trial of the Supreme Court Justice Samuel Chase — one of the most explosive political episodes of the Jefferson administration — that “the officers liable to impeachment” are “the president, the vice president and all civil officers of government.”
The last point to make here comes from still another amicus brief, this one prepared and filed by the historians Jill Lepore, Drew Gilpin Faust, David Blight and John Fabian Witt. Section 3, they note, was not written for the past; it was written for the future. “In the 14th Amendment the United States now possessed the blueprint of a new Constitution, a new kind of federalism, a commitment to equality before the law, and a method to legally guarantee the essential results of the Civil War,” they write. “That blueprint included prohibiting past officeholders from holding federal or state office after engaging in an insurrection against the Constitution.”
This was recognized at the time. “The language of this section is so framed as to disenfranchise from office the leaders of the past rebellion as well as the leaders of any rebellion hereafter to come,” Senator John B. Henderson of Missouri said, as he cast his vote for the amendment.