By Panu Wongcha-um

BANGKOK (Reuters) -When Sakda Vicheansil, a lawmaker from western Thailand, announced his resignation from the ruling Pheu Thai party in early September, his words reflected the extraordinary decline of the country's most dominant politician, Thaksin Shinawatra.

"Thai people across the country, and especially in my constituency - Kanchanaburi, Constituency 4 - are suffering," he said on Facebook.

"The government has completely failed to resolve their problems."

Former premier Thaksin, 76, has run a populist vote-winning machine in Southeast Asia's second-largest economy for a quarter century but his grip on electoral politics has finally slipped, analysts said.

Outmanoeuvred by a smaller former coalition partner, and with a daughter sacked as prime minister and his once dominant party desperately asking the king to endorse a snap election that it would struggle to win, the billionaire Thaksin is on the ropes.

Late on Thursday, a day before a parliamentary vote to pick the next premier, Thaksin - who has previously fled into exile - flew out of Thailand on a private jet, without making any public comment and fueling speculation about his intentions.

In a post on X, he said he was in Dubai for a medical checkup and would return within days.

"For all intents and purposes, the Shinawatra family is politically spent," said Thitinan Pongsudhirak, a political........

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