The Wall Street Journal's editorial board is sounding the alarm ahead of President Donald Trump's summit with Chinese President Xi Jinping in Beijing on Thursday, warning that Xi set a "Venus fly trap" for Trump on Taiwan that could upend decades of U.S. foreign policy.The board warned that Xi wants Trump to formally "oppose" Taiwanese independence, a subtle but seismic shift from the current U.S. posture of "not supporting" it. While the change might sound like diplomatic hairsplitting, the Journal warned it would have massive ramifications."Mr. Xi will argue the tweak is of no great consequence to Americans and stroke Mr. Trump’s ego that he can bring peace to one more troubled region," the board wrote. "Yet that change would disrupt decades of U.S. policy that, for all its delicate diplomatic wording, has held the peace. Taiwan is not the aggressor in the Taiwan Strait, a Xi fiction that 'opposing independence' would indulge."Japan and other U.S. allies in the region are anxiously watching the summit, the board noted, as U.S. credibility on Taiwan is linked to other alliances in Asia.The Journal also warned Trump not to expect much from planned AI arms control discussions with Beijing, noting that the Trump administration itself had warned this year that China is engaged in "industrial-scale" theft of American AI models.On Iran, the board urged Trump to ask Xi directly whether China is helping Iran with intelligence — a pointed question given Beijing's role as a key financier of the world's bad actors, from Russia to Iran and North Korea.