Donald Trump is the master of the Taunting Tweet. Whether he is taking on the Democrats, Republicans or even members of his own cabinet like Jeff Sessions, he is pretty handy with the snarky, cutting comment.

To be sure, there have been plenty of Tweets tweaking Trump, but none of them are from anyone he cares about.

So it must have been particularly galling for Trump to read the Russian prime minister’s Tweet that his administration is showing “total weakness” in the “most humiliating way.” To have his buddies the Russians publicly proclaim him as “an incompetent player” (Facebook post) has to be the ultimate insult for smart, tough guy Trump. Truly humiliating.

Of course, there may be more to it behind the scenes. The best way to gauge Trump’s relations with the Russians is to follow the money. Is Russian financing still flowing to the Trump family of companies? Is Trump Inc. doing any new real estate development in Russia? We might have to wait until Robert Mueller speaks before we find out.