This series of events is at least somewhat plausible, Trump's credibility (or lack thereof) notwithstanding. Remember that those allegations of Chinese weapons going to Iran came from Western media, not Chinese sources. I am quite skeptical that such involvement was ever on the table in Beijing. It costs nothing to reassure Trump.
WASHINGTON, April 15 (Reuters) - Donald Trump asked Chinese President Xi Jinping in a letter not to weapons, and Xi responded that China was not supplying Tehran, the U.S. president told Fox Business Network in an interview that aired on Wednesday. Trump, in the interview taped on Tuesday, did not say when the letters were exchanged. Last week, he threatened countries with an immediate if they supplied Iran with weapons.
"I wrote him a letter asking him not to do that, and he wrote me a letter saying that, essentially, he's not doing that," Trump told FBN's "Mornings with Maria" program.