"McArthur didn't act like he was President ;-)"
MacArthur paid a price for that, as I recall.
AND the country.
One assumes MacArthur having fought under FDR for 12 years felt Truman was a pretender, and not capable of grasping the military ramifications in the Chinese/Korean arena. MacArthur wound up correct (unfortunately for the 50,000 Americans who died in Korea.)
Both Truman and Nixon were the Rodney Dangerfields of U.S. Presidents.