This will be Trump’s second meeting with the Chinese leader. Their first, held in April at Trump’s resort in Mar-a-lago, Florida, ended with unexpected affirmations of bonhomie. “We had great chemistry,” Trump boasted after that encounter. “I liked him and he liked me a lot.” But the chemistry this time may prove combustible.

Over the past two weeks, Trump has signaled his growing exasperation with Xi for China’s failure to pressure North Korean strongman Kim Jong-un to abandon his quest to develop nuclear missiles capable of striking the United States. The first hint of trouble came in a backhanded Trump tweet: “While I greatly appreciate the efforts of President Xi & China to help with North Korea, it has not worked out. At least I know China tried!”

Twits followed tweets. Over the past week the U.S. has slapped sanctions on the China-based Bank of Dandong for helping North Korea to finance its weapons programs; announced $1.4 billion in arms sales to Taiwan; and conducted “freedom-of-navigation operations” within 12 nautical miles of Triton, an island in the South China Sea that is occupied by China but claimed by Vietnam. The State Department also placed China on its global list of the worst offenders in human trafficking, and senior U.S. officials renewed trade threats against Beijing including steep tariffs on Chinese steel imports.

China expressed “outrage” at the arms sales to Taiwan, but mostly held its fire. Not so Kim Jong-un. On July 4, the Dear Leader supervised the launch of Pyongyang’s first intercontinental ballistic missile, a weapon experts say demonstrates North Korea ability to lob nukes as far as Alaska. Kim described the missile test as an Independence Day “gift” for the “American bastards.”

Suddenly the Trump – Xi tryst looks as lasting as a Taylor Swift fling. “Where did the bromance go?” lamented Hong Kong’s South China Morning Post. “The surprise is not that the honeymoon has come to an end but that there was ever one at all,” tsked the Economist.

Among global pundits there’s an emerging consensus that the relationship was “doomed” from the start because of “illusions” on all sides. Huang Jing, an expert at the National University of Singapore, says Xi was “rather naive” to imagine he could mollify Trump with minor trade concessions and personal charm. He thinks “Trump is a weak and embattled leader” beholden to conservatives who will crucify him if he goes soft on China.

Others fault Trump for imagining he could prod Xi to risk destabilizing an unpredictable neighbor just as the Communist Party is preparing for a crucial meeting to pick its next generation of leaders. Eurasia Group’s Evan Medeiros says Xi “can’t don’t anything, commit to anything, that could create a political vulnerability for him” ahead of fall’s 19th party congress.

Some say Trump was doubly foolish to assume Xi had any real leverage over Kim in the first place. Many China-based global executives share the view of Paul Haenle, director of the Carnegie-Tsinghua Center in Beijing, who argues Trump’s decision to make North Korea the “singular focus” of U.S.-China relations has proved “naive and ineffectual.”

As the New Yorker’s Evan Osnos puts it, both sides have been operating on different wavelengths, talking to each other but not really communicating—a phenomenon the Chinese describe as “a chicken talking to a duck.”

So what now? US secretary of state Rex Tillerson insisted yesterday that Trump has “not given up hope” on Beijing. He acknowledged Chinese efforts to convince North Korea to abandon its nuclear program had been “uneven” but stressed that last week’s sanctions “certainly got [China’s] attention.” New York Times columnist Bret Stephens makes a good case for why Trump’s new get-tough policy with China might actually be “on the right track.”

We’ll see. But the outcome of today’s meeting is anybody’s guess. Stay tuned!