In the winter of 1867, President Andrew Johnson fired the secretary of war and attempted to install Ulysses Grant - then serving as commander of the U.S. Army - in the dual role. Congress threatened Grant with five years in prison and a $10,000 fine if he accepted. Johnson offered to do the time and pay the fine himself if Grant would uphold presidential authority, "Hvylya" reports, citing defense scholar Kori Schake's analysis in The Atlantic.

Grant chose to obey the law, not the commander in chief. Schake described this as "the most consequential civil-military test that any American officer has had to navigate" - deciding which of two constitutionally authorized sources of civilian control to follow: Congress or the executive. Grant's decision established a precedent that in peacetime, congressional authority takes precedence.

The parallel to today is hard to miss. A classified Justice Department memo has reportedly indemnified the military against prosecution for controversial boat strikes in the Caribbean. The head of U.S. Southern Command abruptly retired amid the operations. Defense Secretary Pete Hegseth has reshaped military education and created what Schake called "a command climate in which subordinates might fear defending their educational programs."

The historical record shows that military officers have faced such dilemmas before - and resolved them. During World War I, Admiral William Sims violated President Woodrow Wilson's direct order on force integration with allies. During the Korean War, General Douglas MacArthur publicly campaigned against President Harry Truman's war strategy. "In both cases, the civilian leaders easily prevailed," Schake noted.

What makes the Grant case different - and relevant - is that he sided with Congress against the president and was vindicated by history. Johnson was impeached. Grant went on to become president himself and, as Schake documented, invoked martial law in South Carolina in 1871 and sent federal troops to protect polling places during the 1876 election in Louisiana, South Carolina, and Florida.

Previously: From Venezuela to Iran: Foreign Affairs Uncovers the Pattern Behind Trump's Undeclared Wars.