The generation of political figures that reached the White House during the last one-third of the 19th century, with one exception, consisted entirely of veterans with substantial military records. Only the Democrat Grover Cleveland had remained a civilian, even though of military age, during the Civil War (not especially committed to the Union cause, he paid for a substitute to avoid serving). Theodore Roosevelt, an infant during that conflict, rose to the rank of colonel of volunteers as the Rough Rider hero of the Spanish-American War and followed the assassinated McKinley in office in 1901.
After Roosevelt left the Presidency in 1909, the nation experienced a long hiatus in the advent of veterans to America's highest political office. Not until 1945 with the inauguration of Harry S. Truman, a National Guard artillery officer in France during World War I, did a chief executive with a stint in the armed forces again became President. But Truman led off a procession of no fewer than nine Presidents in a row with veteran's status: He was followed by Eisenhower, Kennedy, Lyndon Johnson, Richard M. Nixon, Gerald R. Ford, Jimmy Carter, Reagan, and Bush. All but Truman and Carter, the latter a career naval officer from 1947 to the end of the Korean War in 1953, were World War II veterans (Eisenhower also was on active duty as an army officer during the First World War). All but Eisenhower, a long-service West Pointer, held relatively junior rank. All but Reagan saw overseas duty and two -- Kennedy and Bush -- distinguished themselves as junior officers by gallantry in combat.
It's hard to argue that FDR needed military service to have a strong presence or to instill discipline. Similarly, Ford's and Carter's military service didn't seem to enable them to connect with enough people to govern from a position of strength.
It's a bogus argument that Keillor puts forth. While there are good arguments for national service of some sort, requiring a person have "military experience" to be president is a bad idea.
Cheers,
Scott.