"Move Forward chooses an uncompromising mode of change while Pheu Thai choose a compromising mode of change," Prajak said. Pheu Thai has been far more measured in its messaging on the monarchy - and that could leave it with more options. "Pheu Thai is holding its cards close to its chest," said Thitinan Pongsudhirak, a political scientist at Bangkok's Chulalongkorn University. "I think Pheu Thai will stick with Move Forward," he said, adding abandoning its ally would make Pheu Thai look as if it was betraying the will of the people. "I still think that a conservative coalition ... with Senate backing is far more likely to emerge than a pro-democracy led coalition," Abuza said.

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