No Senator or Representative shall, during the Time for which he was elected, be appointed to any civil Office under the Authority of the United States which shall have been created, or the Emoluments whereof shall have been increased during such time; and no Person holding any Office under the United States, shall be a Member of either House during his Continuance in Office.Senator Clinton was a member of Congress in January of 2007, when cabinet salaries were increased by an Act of Congress from $186,600 to $191,300. A salary is an "emolument" of office, and therefore no sitting member of Congress is eligible for a Cabinet position.
Now, this is not the first time the problem has come up. In 1973, President Nixon wanted Ohio Senator William Saxbe to be Attorney General; Saxbe had voted in 1969 to increase the Attorney General's pay. The "fix" to this problem was for Saxbe to voluntarily accept the pre-1969 salary and remit the raise. This was, however, condemned by Democrats as Constitutionally suspect and a strict construction of the Enoluments Clause would suggest that those Democrats were right.
It's safe to say that Senator Clinton does not care about the $4,700.
The strictest construction of the Enoluments Clause would be that any Member of Congress who votes on (or even against) a pay raise for any executive office is thereby barred, forever, from holding that office. Since the Enoluments Clause applies to both elective and appointed positions, that would seem to apply to the offices of President, because Congress fixes the salary of the President, too. (The Vice-President's salary is now treated as a high-level civil service job for compensation purposes, and is equal to the salary paid to the Speaker of the House. Thus, the Vice-President's salary is at the moment beyond the reach of the Enoluments Clause, but that could theoretically change.)
And, the Twenty-Seventh Amendment now makes an exception to the Enoluments Clause in that a Member of Congress can vote a raise for his or her own seat, provided that the raise does not take effect until the next term of office.
Most recently, George Bush, and Al Gore would not have been affected by the Enoluments Clause because they were not sitting Members of Congress in 2000. But John McCain would debatably have been barred from assuming the Presidency had he won the 2000 Republican nominations and then the general election, having served in the Congress that voted in the 2001 pay raise, and debatably, John Kerry would have been ineligible to serve as President had he won election in 2004. Nor is Senator Obama barred from becoming President Obama, because he was not a Member of Congress in 1999. Joe Biden was a Member in 1999, but he is becoming Vice-President, and that is a civil service salary not enlarged (directly) by Congress.
Now, here's the interesting scenario. Let's say in a year, "something happens" to Obama, and Joe Biden has to become President. In 1999, Joe Biden served in a Congress that voted a salary increase for the President. Is he now barred from assuming that office by virtue of the Enoluments Clause?
One sidestep to this might be to say that Biden would be neither "elected" President nor "appointed" President in that case. Rather, he would "succeed" or "accede" to the office.
But I don't think that this sort of wordplay is really what was intended by the Framers. The Framers wanted to keep Members of Congress from creating sinecures for themselves. They surely knew that Members of Congress would be considered for the Presidency and for Executive positions, and indeed it has happened many, many times in our history that sitting Members have been recruited into an Adminsitration (and sometimes elected into one).
Still, if you want to be technical about it, this is an operative part of the Constitution, and it says what it says. The historical precedent has been a sidestep by way of foregoing a salary, not any sort of interpretation of the Clause itself. And so a strict reading of the Constitution is such that Biden cannot become President if Obama dies in office, and Hillary Clinton cannot serve as Secretary of State.
(P.S. Careful Readers will note the creation of a "Joe Biden" tag, which has been retroactively applied to all posts concerning the Vice-President-Elect.)