Section 1 of the 20th Amendment:

The terms of the President and Vice President shall end at noon on the 20th day of January, and the terms of Senators and Representatives at noon on the 3d day of January, of the years in which such terms would have ended if this article had not been ratified; and the terms of their successors shall then begin.

Okay.  So Bush and Cheney stopped being President and Vice-President at the stroke of noon.  But because things were running behind schedule, Obama had not taken the oath.  He wasn't sworn in until 12:03, because YoYo Ma & Friends were still fiddling around. 

But if Bush and Cheney weren't President, then was Obama automatically President during those minutes? 

It would seem so ("the terms of their successors shall then begin").

But wait. Article II, Section 1 states the following:

Before he enter on the execution of his office, he shall take the following oath or affirmation:–"I do solemnly swear (or affirm) that I will faithfully execute the office of President of the United States, and will to the best of my ability, preserve, protect and defend the Constitution of the United States."

So there is  a gray area here.  Is the oath a pre-requisite to being President (along with the 12:00 noon requirement)?

One could argue that Obama became President at noon, but he could not execute the duties of that office until he took the oath.  In other words, he was a powerless leader for a prescious few minutes.

But there are other views.  Professor Ken Katkin, a constitutional law professor, makes an interesting argument, and comes to an interesting conclusion:

(1) The 20th Amendment provides that “[t]he terms of the President and Vice President shall end at noon on the 20th day of January. . . . ”

(2) Art II., Sec. 1 Cl. 8 provides that “[b]efore he enter on the Execution of his Office, [The President] shall take the following oath. . . ”

(3) President Obama did not take the Oath of Office until about 12:03 pm today, after Vice President Biden took it at about 12:01 p.m.

(4) Therefore, there was a brief window (just after noon) when George Bush and Dick Cheney were no longer President and Vice President, but Barack Obama and Joe Biden also were not yet qualified to enter on the Execution of their offices.

(5) The Presidential Succession Act, 3 U.S.C. sec. 19(a)(1), provides: “If, by reason of . . . failure to qualify, there is neither a President nor Vice President to discharge the powers and duties of the office of President, then the Speaker of the House of Representatives shall, upon his resignation as Speaker and as Representative in Congress, act as President.” Section 19(b) states that the President Pro Tempore of the Senate shall act as President (under the same terms and conditions) if the Speaker of the House fails to qualify.

(6) Neither Nancy Pelosi nor Robert Byrd actually resigned their seats in the Congress. Thus, neither of them qualified to become Acting President under the Presidential Succession Act. Plus, interbranch appointments might be unconstitutional anyhow. See Akhil Reed Amar and Vikram David Amar, Is the Presidential Succession Law Constitutional?, 48 Stan. L. Rev. 113 (1995); but see Howard Wasserman, Structural Principles and Presidential Succession, 90 Ky. L.J. 345 (2002).

(7) Section 19(d)(1) of the Presidential Succession Act provides: “If, by reason of . . . failure to qualify, there is no President pro tempore to act as President under subsection (b) of this section, then the officer of the United States who is highest on the following list, and who is not under disability to discharge the powers and duties of the office of President shall act as President: Secretary of State . . . ”

(8) Notably, Section 19(d)(1) does not condition the Secretary of State’s assumption of the powers and duties of the office of President on resignation of her current office, nor does elevation of the Secretary of State raise any constitutional issue of interbranch appointment.

(9) The term of office of the Secretary of State does not automatically terminate at noon on the 20th day of January.

(10) On January 20, 2009, Condoleeza Rice was (and is) still the Secretary of State.

(11) Accordingly, from 12:00 noon until 12:01 p.m. (when Vice President Biden took the oath of office and became Vice President), Condoleeza Rice was momentarily the Acting President of the United States, our first African-American President.

Sadly, Katkin is wrong on his timing.  Biden was not sworn in at 12:01 p.m.; he was sworn in before noon (before Yoyo Ma and Perlman played).  So, presumably, Joe Biden was President for a few minutes under the Presidential Succession Act.

The academic issue gets thornier when you consider that President Obama did not take the presidential oath as written.  In giving the oath, Chief Justice Roberts misplaced the word "faithfully".  He corrected himself, but Obama repeated the words as Roberts initially said them, an an awkward crosstalk between the two.

The obvious solution to this minor problem is for the oath to be re-administered.  It takes 30 seconds, and can be done in private.  In fact, Charles Cooper, head of the Justice Department's Office of Legal Counsel under President Ronald Reagan, said that he would be surprised if the oath hadn't already been re-administered.

Assming that the oath has not been re-administered, then our President is Joe Biden.

But don't get your hopes up, conspiracy theorists.  Legal challenges to Obama's presidency won't survive.  Lyle Denniston explains why.

UPDATE:  Some believe that, as a matter of tradition, an incoming President takes the oath of office privately before the official ceremony.  There's no knowing if Obama did this.  If he did, then of course, everything in this post is moot.