The twilight of King Bhumibol Adulyadej’s reign has heightened Thailand’s political conflict, both in terms of the palace’s inability to adjudicate and the jockeying for power under his successor. King Bhumibol is 86 and in poor health. He rarely appears in public, but continues to enjoy adulation from ordinary Thais.

Many look askance at his anointed successor, Crown Prince Maha Vajiralongkorn. The prince, an Air Force pilot, has assumed more royal duties and greater powers within the military, which is entwined with the palace. But he lacks the popularity of his younger sister, Princess Maha Chakri Sirindhorn, who scholars say also has a claim to the throne under opaque succession laws.

Palace courtiers have long suspected Thaksin Shinawatra, the former prime minister, of currying favor with the prince. Fear of such an alliance has fueled calls for Princess Sirindhorn to instead ascend the throne.

“The palace is afraid of Thaksin. He’s powerful and popular. And the palace is declining,” says Thongchai Winichakul, a historian at the University of Wisconsin-Madison.

This purported rivalry may have fed the recent turmoil, says Paul Handley, author of “The King Never Smiles,” a 2006 biography of the king that is banned in Thailand. Some pro-Thaksin demonstrators reportedly wore shirts emblazoned with the number of the prince’s Army unit; some soldiers who seized power in May wore purple armbands denoting loyalty to the princess.

“It’s becoming a public issue. And succession should never be a public matter,” Mr. Handley says.

In fact, there is virtually no public debate in Thailand over the king’s successor or what sort of role the palace should play. Strict laws prevent any criticism of the monarch and his family, and courts have handed down increasingly long jail terms to offenders.

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Still, in recent years criticism has grown over the palace’s lavish spending.

Forbes ranked the king as the world’s richest monarch. Much of this wealth derives from land and stock held by the Crown Property Bureau, a quasi-public company