Trump derangement syndrome (TDS) is a pejorative term used to describe negative reactions to U.S. President Donald Trump that are characterized as irrational and disconnected from Trump's actual policy positions. The term has mainly been used by Trump supporters to discredit criticism of him, as a way of reframing the discussion by suggesting that his opponents are incapable of accurately perceiving the world, thus making TDS a logical fallacy. Some journalists have used the term to call for restraint when judging Trump's statements and actions. The term has also come to be used to describe the nature of Trump supporters in their unwavering support of the president.

Despite the usage of the term syndrome suggesting a medical condition, TDS is not an official medical diagnosis. Trump derangement syndrome is not recognized as a legitimate mental disorder by any version or draft of the Diagnostic and Statistical Manual of Mental Disorders of the American Psychiatric Association or by law in any U.S. state.

The origin of the term is traced to Charles Krauthammer, a conservative political columnist, commentator, and psychiatrist, who coined the phrase Bush derangement syndrome in 2003 during the presidency of George W. Bush. That "syndrome" was defined by Krauthammer as "the acute onset of paranoia in otherwise normal people in reaction to the policies, the presidency—nay—the very existence of George W. Bush".

Similarly, conservative activist David Horowitz used the phrase "Obama derangement syndrome" to compare "over-the-top hysteria" in the criticism offered by sections of the right-wing commentariat regarding Barack Obama following the latter's election as president to Bush derangement syndrome, citing comparisons of Obama to Stalin, David Koresh, Charles Manson and Saddam Hussein, although Krauthammer disagreed with Horowitz's use of the phrase. Horowitz particularly applied the phrase to those who advocated "birtherist" conspiracy theories that claimed Obama was not a native-born United States citizen. Ezra Klein has argued that whilst those accused of Bush derangement syndrome was inspired by opposition to Bush's policies, those acccused of Obama Derangement Syndrome were driven by reactions to Obama as an individual, in particular his race and Kenyan heritage, and a feeling among some conservatives that these made him un-American.

The first use of the term Trump derangement syndrome may have been by Esther Goldberg in an August 2015 op-ed in The American Spectator; she applied the term to "Ruling Class Republicans" who are dismissive or contemptuous of Trump. Krauthammer, in an op-ed commented that—in addition to general hysteria about Trump—the "Trump Derangement Syndrome" was the "inability to distinguish between legitimate policy differences and ... signs of psychic pathology".

According to The Independent, "the highly-politicized term" was coined to dismiss criticism of Trump in his first term as liberal hysteria, suggesting that people abandon all logic and reason due to their dislike of the president.

Fareed Zakaria defined the term as "hatred of President Trump so intense that it impairs people's judgment". CNN's editor-at-large Chris Cillizza called TDS "the preferred nomenclature of Trump defenders who view those who oppose him and his policies as nothing more than the blind hatred of those who preach tolerance and free speech". Pointing to previous allegations of Bush derangement syndrome and Obama derangement syndrome, Cillizza suggested, "Viewed more broadly, the rise of presidential derangement syndromes is a function of increased polarization—not to mention our national self-sorting—at work in the country today." Bret Stephens has described the term as something used by conservative groups whenever someone speaks out critically against Trump, regardless of political affiliation.

CNN political analyst John Avlon uses the term in a more generalized sense inclusive of positive emotions as well as hatred towards Trump, so that for example, TDS accounts for denialism about Trump's defeat in the 2020 election, as a "political diagnosis" of people who "simply can't accept the fact that he lost the election". This new definition derogatorily describing the nature of Trump supporters rather than his deriders has been picked up by others and widely used.