On Tuesday, February 2, PBS’s American Experience will air “Murder of a President,” a two-hour documentary about the 1881 assassination of President James A. Garfield. The film is based on author Candice Millard’s 2011 bestseller Destiny of the Republic: A Tale of Madness, Medicine and the Murder of a President. Millard and other writers, including Allan Peskin, Kenneth D. Ackerman, and Charles E. Rosenberg before her, have tried to get inside the mind of the assassin Charles J. Guiteau. There is little doubt that Guiteau was mentally ill, but books that dismiss him as merely a “disappointed office seeker” greatly oversimplify the state of the Republican Party at the time and ignore Guiteau’s very political motivations for shooting Garfield.

When police apprehended Charles Guiteau immediately after he shot Garfield on July 2, 1881, Guiteau calmly told them, “I am a Stalwart and Arthur will be president.” These were not just the ramblings of a mentally unbalanced murderer. They revealed that Garfield’s murder was prompted by politics.

In 1881, the Republican Party had split into two factions. What divided them was patronage, or what was known as the “spoils system,” for to the victor go the spoils. Under the patronage system, the winners of congressional and presidential elections had the power to appoint whomever they chose to fill numerous federal jobs. Experience and qualifications mattered little (if at all); what mattered was that those appointees would vote for the men who appointed them and thus keep that party—or faction—in power. Politicians loved the system because it allowed them to put friends and relatives into lucrative positions and ensure loyalty from everyone they appointed. Senator Roscoe Conkling of New York was the leader of the faction known as the “Stalwarts.” He was the undisputed king of the patronage system, and the key weapon in his spoils arsenal was the position of Collector of the Port of New York.

Much of the nation’s trade flowed through the Port of New York. Because the Collector of Customs received a percentage of the customs duties, the job was the most prized appointment in the country. The man who held it was a key player in controlling the state of New York, whose electoral votes were crucial to winning the White House. Roscoe Conkling demanded that he alone select the man to fill this politically important and personally lucrative position. During his term, President Rutherford B. Hayes, seeking to wrest control from Conkling, nominated two different men as Collector. Conkling rallied his Senate colleagues to defeat both and eventually succeeded in getting his own choice, an acolyte named Chester Alan Arthur, appointed instead. In 1878, President Hayes fired Arthur from his position for turning a blind eye to corruption inside the Customs House. In response, Conkling had Arthur named chairman of the New York Republican committee and made plans to have Arthur elected as the junior U.S. Senator from New York in 1880.

In the 1880 election, Stalwarts led by Conkling encouraged former president Ulysses S. Grant to seek an unprecedented third term in the White House. Despite the many scandals of Grant’s two previous terms (1869-1877), the former Union general was still immensely popular with the American public. In consultation with Conkling and other Stalwart allies, Grant agreed to run again. Conkling looked forward to reclaiming control of the New York Customs House and once again serving as President Grant’s right hand man, just as he had done during the earlier Grant administrations.

The other Republican faction, dubbed “Half Breeds,” supported Maine Senator James G. Blaine for the presidential nomination. While historians have tried to dress up the factionalism in a principled fight over the spoils system, the real breach between the two camps was personal hatred between Conkling and Blaine, dating back to their early service together in the House of Representatives during the Civil War. They could not work together, and each man wanted control of the government for himself.

At the Republican convention in Chicago, Half Breeds worked tirelessly to block Grant’s nomination. In turn, the Stalwarts refused to support Blaine. After the first several ballots, it was clear that neither man could obtain the necessary votes to capture the nomination. But members of both factions liked and respected James A. Garfield of Ohio, longtime member of the House of Representatives and currently Ohio Senator-elect. On the 36th ballot, Garfield, still stunned that his name had been forwarded as a candidate at all, received the nomination. The Half Breeds were the faction most in favor of Garfield, so to appease the Stalwart faction, Conkling disciple Chester A. Arthur, just two years removed from his New York Customs House firing, received the party’s vice presidential nomination.

Garfield went on to defeat Democrat Winfield Scott Hancock by a razor-thin popular vote margin—about 8000 votes– in the 1880 election and assumed the presidency on March 4, 1881. If the Arthur nomination was intended to be an olive branch to the Stalwarts, that branch cracked when Garfield made James Blaine his Secretary of State. The branch then splintered when the new president nominated William H. Robertson to be Collector of the Port of New York without consulting Conkling. Historian Heather Cox Richardson notes that Conkling was “a famously touchy character” and that he was “undoubtedly personally affronted.” However, as Richardson points out, Conkling opposed Robertson’s nomination by claiming that the Senate’s role to advise and consent to presidential appointments gave senators the power of appointment itself. “What was really at stake,” writes Richardson, “was whether or not Conkling would control New York.” And since New York’s electoral votes controlled the White House, whether he or Garfield would control the country.

Conkling devised a bold plan to force the issue and embarrass President Garfield. He and New York’s junior senator, Thomas Platt, resigned their seats in protest, fully confident that the New York legislature would immediately reappoint them. Conkling and Platt miscalculated; the legislature was happy to be rid of them and promptly elected others to fill their seats. The Senate confirmed Robertson as head of the New York Customs House, and James A. Garfield won the key political victory of his very brief term in the White House.

But the story wasn’t over. Charles Guiteau considered himself a Stalwart Republican. He had supported U.S. Grant for the party’s nomination in 1880, even preparing a nonsensical speech he hoped to give for the Grant campaign throughout New York. When the Republicans ended up choosing Garfield instead, Guiteau simply crossed out all references to “Grant” in his speech’s text and replaced them with “Garfield.” During the campaign, Guiteau hounded Republican officials to let him give his speech, which he finally did to a puzzled New York City crowd. This odd performance led the mentally unbalanced Guiteau to believe that he had helped Garfield win New York, the most coveted electoral prize of the 1880 contest and the state that put Garfield over the top and into the presidency. Guiteau’s contribution to the party’s victory entitled him, he felt, to a patronage position, and he soon went to Washington, D.C. to present himself for consideration for the American consulship to Paris. He had no skills, qualifications, or experience to warrant such a position, but lesser men had received prized jobs under the patronage system.

Guiteau was disappointed. His efforts to secure the Paris appointment failed, and he became a nuisance to the new administration. He aroused the ire of Secretary of State Blaine, who at one point thundered at Guiteau, “Do not ask me about the Paris consulship ever again!” Once Guiteau realized that he would not get the position he wanted, he decided (with encouragement from God, he claimed) that removing Garfield was imperative. Making Chester A. Arthur president would save the country from a Half Breed Republican like Garfield and put Arthur and patronage king Roscoe Conkling into power. Guiteau would also surely receive the Paris consulship from a grateful President Arthur.

Guiteau bought a pistol and stalked President Garfield around Washington before finally shooting him on July 2, 1881. Garfield lingered for eighty days and suffered horrific medical treatment before dying on September 19. Rather than being heralded as a hero for saving the Republican Party, Charles J. Guiteau was incarcerated, tried, and found guilty of murder. (In what was probably one of the most lucid statements he ever made, Guiteau, when accused of murdering Garfield during his trial, replied, “The doctors did that. I merely shot at him.”)

Guiteau was hanged on June 30, 1882. He died a “disappointed office seeker,” to be sure, but to describe him as that and nothing more only tells part of the story. He was clearly mentally ill, but was also a political assassin that killed President Garfield in an attempt to change the faction in power. The Republican Party’s factionalism, clearly responsible for the selection of Garfield as its standard bearer in 1880, also led to the President’s murder at Guiteau’s hands.