I think the analogy JMS had in mind for Sheridan's position with the IA was Washington's position with the new United States. The Alliance is a "more perfect union" of the various races, going beyond the old League and the B5 Council. Similarly the Constitution established a Federal Government that went far beyond what was provided by the original articles of confederation.
In case of the U.S. Constitution there were certainly - and in the case of the IA there were probably - considerable misgivings about the amount of power the new organization, and especially its president, would wield. One reason that the Constitution was passed by the convention with both a strong central government and a strong executive is that everyone present at the debates knew perfectly well that George Washington would be first to hold the office of President. They trusted him to establish proper precendents, and not to abuse his power. He had, after all, turned down what was effectively an offer to make him King after the revolution. Sheridan similarly did not make himself President of EarthGov following the Civil War - which he certainly could have. Instead he submitted to the judgment of the lawful civil authority and his military superiors. People just love handing power to those who don't seem to want it.
Washington could have remained as President for life, had he chosen. One of the first precedents he established for the office was to decline to accept a third term, an example which held until Franklin Roosevelt and the twin emergencies of the depression and WWII. (A Constitutional ammendment has since made such serial terms impossible, restoring Washington's plan for his successors.)
Most people were comfortable with Washington at the helm,
and nobody was thrilled with his most likely successors (the very next election was the first to be decided in the House of Representatives, if I remember correctly, which will give you an idea how closely things were split.) Washington had been elected unanimously. Sheridan could similarly be seen as the one man that everybody trusted. Even Delenn might be suspected of being too partial to the Minbari. But Sheridan had burned many of his bridges with Earth, and was always scrupulously fair in his dealings with the other races. The notion that "if it ain't broke, don't fix it" probably played a part in his repeated election to the Presidency.
Indications within the show are that the President of EarthGov serves for five years. If the IA adopted the same term of office, Sheridan would have been re-elected in 2266 and 2271, then declined to run in 2276. Delenn would have been sworn in around 2277. (Assuming the President's term starts around New Year's day, and that the elections are held some weeks or months before this.) But I seem to recall Ivanova saying something about what a good job Delenn has done, "these past two years", which suggests that she didn't become President until 2278 or '79 - allowing for some imprecision on Ivanova's part in casual conversation. Kosh will probably remember something from the Centauri Trilogy that sheds some light on this. IIRC Sheridan is still President in 2278 when he and Delenn travel to Centauri Prime in search of David.
If the term is of six or seven years, the math works out a little neater. In any event I don't think that Sheridan served more than three terms, and it is even possible that he resigned in favor of Delenn before the end of his last term, and that she was later elected in her own right.
Regards,
Joe
