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The Federated States of Micronesia has had 7 presidents since 1979.
As of May, 2012 there have been 11 U. S. Presidents since Harry Truman.
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Including the one in office in 1920 and up to and including Barack Obama, there have been 17 U.S. Presidents.
It has been 66 years from 1946 to 2011 :)
There has been only two democratic presidents elected since Ronald Reagan, they are Bill Clinton and Barack Obama.
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There have been a total of 10 presidents of Ireland since the office was established in 1938. Before that, Ireland was part of the United Kingdom and did not have a presidential system. Therefore, since the 1780s, there have been no Irish presidents, as the position did not exist until the 20th century.