From the wonderful Dave Pell newsletter:

“We informed the White House this morning that I will not attend the work meeting scheduled for next Tuesday.” That was Mexican President Enrique Peña Nieto letting the world know he had canceled his planned trip to the US over Trump’s insistence on building a wall, and further insistence that Mexico will pay for it. The message was delivered via a tweet, and was (of course) met with counter-tweets from the Oval Office. Social media spats and flame wars now have serious diplomatic ramifications. What were once harmless exchanges between a couple of bad hombres can now cause geopolitical shifts. (Sometimes I think the whole Trump presidency is part of a secret plot to save Twitter.)

Discuss (as they say in history exams).