During his 1944 campaign for President, N.Y. Governor Thomas Dewey argued that permitting Pres. Roosevelt to have a fourth term was a dangerous threat to freedom. Gov. Dewey lost in 1944 and, more famously, in 1948 against Pres. Truman. 
However, Gov. Dewey, with a Republican Congress, managed to get the 22nd Amendment introduced and, ultimately, ratified. This may have backfired.
President Franklin Roosevelt was the first person to win more than two terms. But, he was not the first President to seek a third term. His distant cousin, Theodore, sought a third term. As did others. Rather than threatening freedom and potentially enshrining a de facto monarch, permitting a sitting two-term President to seek a third term served a valuable function in our system of checks and balances.
Presidents Eisenhower, Nixon, Reagan, Clinton, G.W. Bush, and Obama were termed “lame ducks” upon their second election. Prior to this point, no two-term President was a lame duck until he bowed out or the election was lost. Instead of a 2-8 month lame duck period, we now have a 4 year, two month period. But, is he truly a lame duck?
Presidents have done a great many things in their second terms. The Watergate coverup, Iran-Contra, the Lewinsky scandal: to the extent the President himself is alleged to have been involved in a cover-up, that cover-up occurred during the second term. Speaker Boehner has now turned to the courts because he believes Pres. Obama is not faithfully executing the laws. Ultimately, the Court, though, cannot force a President to act, even assuming Speaker Boehner is right and could win. And, even though Congress gets to decide what constitutes “Other High Crimes and Misdemeanors”, impeachment is really a 2nd degree political action–you vote for the people who vote on impeachment. Prior to the 22nd Amendment, second-term Presidents had a check on their power to act (or not act): the third-term campaign. Presidents no longer have to worry about facing the electorate for a third time and can act (or fail to act) with virtual impunity. Such may be a more dangerous threat to freedom than Gov. Dewey imagined.
