Twenty-second Amendment to the United States Constitution
Some argue that the 22nd Amendment and 12th Amendment bar any two-term president from later serving as vice president as well as from succeeding to the presidency from any point in the presidential line of succession. Others contend that the original intent of the 12th Amendment concerns qualification for "service" (age, residence, and citizenship), while the 22nd Amendment, concerns qualifications for "election", and thus (strictly applying the text) a former two-term president is still eligible to "serve" as vice president (neither amendment restricts the number of times an individual can be elected to the vice presidency), and then succeed to the presidency to serve out the balance of the term (though prohibited from running for election to an additional term).
First 100 days of Barack Obama's presidency
According to the Twentieth Amendment to the United States Constitution, Section 1: "The terms of the President and Vice President shall end at noon on the 20th day of January". Thus, Bush had relinquished the Presidency at 12:00. According to the Twentieth Amendment to the United States Constitution, Section 3: If, at the time fixed for the beginning of the term of the President... if the President elect shall have failed to qualify, then the Vice President elect shall act as President until a President shall have qualified." By Article Two, Section 1, Clause 8 of the Constitution and Amendment 20, Some feel that Obama was not able to assume the Presidency until 12:05. In fact, since Obama did not complete his oath until 12:01, there was further speculation as to who was President for the first minute after Bush relinquished control.