Mad Kings

According to tradition, the Roman Republic was preceded by the Kingdom of Rome from 753 BCE to 509 BCE (244 years spanned by just seven kings).

The Roman Republic had lasted for about 482 years after it began with the establishment of the Roman consulate in 509 BCE. 

The first Roman emperor, Augustus, took office in 27 BCE. Tiberius, the second Roman emperor, who took office in 17 CE was reputedly mentally ill, although less flamboyantly that two of his three successors. Caligula, the third Roman emperor, took office in 37 CE. Nero, the fifth Roman emperor, took office in 54 CE.  Two later emperors before the split and then fall of the Roman empire were also considered mentally ill: Commodus who took office in 177 CE and Elagabalus who took office in 218 CE.

The Roman Empire split between the Western and Eastern (Byzantine) empires in 364 CE (391 years after the Roman Empire was established), and the Western Roman Empire fell in 476 CE (112 years after the split).

According to Google AI (I'm feeling lazy today):

The most notable and documented "mad kings" include:

• King Charles VI of France (1368–1422): Often called Charles le Fou (Charles the Mad), he suffered from manic episodes and the infamous "glass delusion," where he believed he was made of brittle glass and wore iron rods in his clothing to prevent himself from shattering. [1, 2]
• King George III of Great Britain (1738–1820): Known as the monarch who "lost America," George III suffered from prolonged bouts of mental instability—long thought to be porphyria—which caused him to experience severe logorrhea and depression, eventually necessitating a regency. [1, 2, 3, 4, 5]
• King Ludwig II of Bavaria (1845–1886): Famously dubbed "Mad King Ludwig," he was deeply eccentric, neglecting state affairs to focus entirely on building extravagantly expensive, fairytale-style palaces (such as Neuschwanstein Castle) before being declared insane. [1, 2, 3, 4]
• King Christian VII of Denmark (1749–1808): Suffering from severe mental illness and paranoia, his inability to govern left his kingdom in the hands of various regents and his royal physician. [1, 2, 3, 4, 5]
• Tsar Ivan IV of Russia (1530–1584): Better known as Ivan the Terrible, his early, capable rule slowly devolved into legendary paranoia and violent, sadistic outbursts later in his life, particularly following the death of his first wife. [1, 2, 3]
• King Nebuchadnezzar II of Babylon (634–562 BC): Often considered the original "mad king," the granddaddy of Babylonian rulers was struck down by a seven-year descent into animal-like insanity as recounted in the Book of Daniel.

In addition to some other European and Middle Eastern mad kings, there are at least two notable ones from Japan (a list that surely omits notable mad Chinese emperors):

• Emperor Yōzei (陽成天皇, Yōzei-tennō, 869–949, ruled 876–884) was described by the 14th-century historian Kitabatake Chikafusa as affected by madness, killing people and animals without reason. His unstable and violent behavior prompted his advisors to force his abdication in 884.^[29]
• Emperor Taishō (大正天皇, Taishō-tennō, 1879–1926, ruled 1912–1926) of Japan, had a variety of neurological disorders, which though at least partially physical in origin incorporated psychological elements as well. Discussion or criticism of an emperor, including that of health issues, remains a controversial subject in Japan for cultural, political, and religious reasons and is referred to as the Chrysanthemum taboo.^[30][31][32]

The United States of America will have persisted for 250 years from its self-declared birthday of July 4, 1776, in a few weeks. Mad kings were a problem that the Founders were familiar with at the time that they drafted the current U.S. Constitution (which took effect in 1789 and added the Bill of Rights in 1791). Indeed, this clear and present danger is the source of some of the emphatic anti-monarchy provisions of the U.S. Constitution.

Probably the most similar historical figures to Trump 2.0 are Nero and Caligula, although there are other somewhat similar examples from European and Asian monarchies.

There is great fear that President Trump signals the end of democracy in America, if not actually on his watch, but showing the way to, and heralding, its end. Then again, while some mad kings were followed by more sane monarchs, others were followed in fairly short order by the demise of the monarchy's power, or its abolition entirely.