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).
Tenure of Office Act (1867)
The act was amended on April 5, 1869, one month and one day after Republican Ulysses S. Grant assumed the presidency. The revisions grew out of an attempt to completely repeal the 1867 act. The measure to repeal passed the House of Representatives with only 16 negative votes but failed in the Senate. The new provisions were significantly less onerous, allowing the President to suspend office holders "in his discretion" and designate replacements while the Senate was in recess, subject only to confirmation of the replacements at the next session. The President no longer had to report his reasons for suspension to the Senate, and the Senate could no longer force reinstatement of suspended office holders.