American democracy works in part because of the calm and violence-free transition of one government to another.

Outgoing President Barack Obama summed it up best after the contentious election of Donald Trump: "The peaceful transition of power is one of the hallmarks of our democracy.”

But the transition between presidents is often fraught with internal conflict.

President-elect Donald Trump's preparation to take over the presidency seems to have its share of problems.

Trump himself prepared little for the possibility of winning the election, out of fear of "jinxing himself." The New York Times has reported that the transition is in "disarray," thanks to infighting and a lack of communication. (Trump has denied the report, saying that the transition was going "so smoothly.")

Transition chair Chris Christie was quickly forced out, reportedly due to conflict with Trump's son-in-law, Jared Kushner, who has taken an outsized role on the Trump transition team.

Trump wouldn't be the first president to assume office after a contentious and problematic transition.

Theres no guarantee that administrations of varying experience and interest levels will mesh well. There's also the matter of a defeated president or party leader teaching his replacement how to do his job.

Many transitions have been perfectly smooth and free of drama. The handover from George W. Bush to Barack Obama is often cited as a model of decorum and preparation.

But it doesn't always work out that way.

Adams to Jefferson, 1800.

Centuries before incoming administrations were given high-tech briefing books and set out to hire thousands of employees, John Adams and Thomas Jefferson fell out over the results of the election of 1800.

The two had gone through a bitter fight that had to be settled in the House of Representatives, with Jefferson winning.

The dispute was resolved peacefully, but by the time Jefferson took the oath of office, Adams had already left Washington. The two wouldn't speak again for nearly two decades.

Buchanan to Lincoln, 1860.

Sixty years later, the transition between outgoing President James Buchanan and newly elected President Abraham Lincoln was a disaster in every conceivable way.

The country was on the verge of the Civil War, and Lincoln's election triggered seven Southern states to secede from the Union.

Buchanan held that these states had no legal right to leave, but that he had no legal right to stop them. Paralyzed, Buchanan did nothing either to prevent or to prepare for the oncoming war, which began a month after Lincoln's inauguration.

Johnson to Grant, 1868. 

Lincoln's successor was involved in transition drama far less disruptive than the Civil War.

Highly unpopular President Andrew Johnson, the first president to be impeached, did not attend the inauguration of his successor, Ulysses S. Grant.

Johnson detested Grant, and the two had a transition period full of snubs and slights.

When the moment came for the men to take a carriage to the ceremony, Johnson refused and took his own carriage out of town.

Hoover to Roosevelt, 1932.

Outgoing President Herbert Hoover and newly elected President Franklin Roosevelt were unable to hide their contempt for each other.

The two had spent their campaign trading insults while the economy crumbled under the Great Depression.

Roosevelt won, and Hoover reached out to him to hammer out joint legislation, but Roosevelt refused, believing Hoover was trying to sabotage him.

They spent the months until March 4 — which was Inauguration Day at the time — sniping in the press. In a final insult, Hoover canceled the traditional pre-inauguration dinner.

It's not surprising that a Constitutional amendment moving the inauguration up was passed during Roosevelt's first term.

Truman to Eisenhower, 1952.

The transition from Harry Truman to Dwight Eisenhower saw another friendship fall apart amid a complex and difficult transition.

Eisenhower was hurt by Truman's insinuation that the general hadn't stood up to the Communist witch hunt of Wisconsin's GOP Sen. Joe McCarthy. Truman believed Eisenhower didn't trust him.

Their transition meetings were perfunctory and terse, and the two argued in the car on the way to the inauguration.

Truman and Eisenhower didn't speak for years afterward.

Bush to Clinton, 1992.

Bill Clinton was involved in rocky transitions both entering and leaving the White House.

The transition from the first Bush administration was marred by a lack of experienced Democratic staffers and problems confirming nominees.

When Clinton left office eight years later, his staff was accused of theft and vandalizing the West Wing.

A president with no political or public experience is coming into office in 2017, so it won't be surprising if the Obama-to-Trump transition winds up one of the most difficult of all time.