About three months ago, after Donald Trump fired then-FBI Director James Comey to derail an ongoing federal investigation, Sen. Richard Blumenthal (D-Conn.) was one of the Democrats raising concerns about the president’s apparent obstruction of justice. That hardly came as a surprise: Blumenthal is a member of the Senate Judiciary Committee and a former prosecutor.

The president, however, apparently saw the Connecticut senator on TV, and soon after launched a Twitter tantrum. “Richie,” Trump said, “devised one of the greatest military frauds in U.S. history.” The president went on and on, lambasting Blumenthal, saying the senator “cried like a baby.”

This morning, Trump saw Blumenthal on television again, and threw the exact same tantrum.

“Interesting to watch Senator Richard Blumenthal of Connecticut talking about hoax Russian collusion when he was a phony Vietnam con artist! Never in U.S. history has anyone lied or defrauded voters like Senator Richard Blumenthal. He told stories about his Vietnam battles and conquests, how brave he was, and it was all a lie. He cried like a baby and begged for forgiveness like a child. Now he judges collusion?”

To the extent that reality still has any meaning, Trump is wrong. Blumenthal spent years in the Marine Corps Reserves, but was not deployed overseas during the war in Vietnam, and he never saw combat. But Blumenthal also never “told stories about his Vietnam battles and conquests” – Trump is just making this up – and the controversy stems from a 2010 story in which the senator apparently slipped at an event, saying he served “in” Vietnam, rather than “during” Vietnam. He apologized for the mistake.

What’s more, this probably isn’t a subject Trump should dwell on: while Blumenthal was in the Marine Reserves, Trump was taking advantage of multiple deferments, thanks in part to a dubious foot injury. The Republican later said avoiding sexually transmitted diseases while dating was his “personal Vietnam.”

But what struck me about this morning’s presidential missives is Trump’s reliance on classic bullying behavior.

On a school playground, a bully will look for another child’s perceived weakness and focus on little else. Maybe the target wears glasses. Maybe he or she is sensitive about weight or height. The merit of the attack doesn’t matter; the bully only cares about its salience: zero in the vulnerability and overcompensate for his or her own insecurities.

For Donald Trump, there’s effectively a file of bullying index cards in his mind, to be used in response to every slight. When he sees Richard Blumenthal, he pulls out the card and says, “Vietnam.” When he sees Sen. Elizabeth Warren (D-Mass.), he reaches into the file and says, “Pocahontas.”

In January, reflecting on the plight of refugees, Senate Minority Leader Chuck Schumer (D-N.Y.) was briefly overcome with emotion. Trump responded by calling him “Cryin’ Chuck” over and over again.

For the president, this is vastly easier than thinking or dealing with the substance of arguments, which says far more about him than those he targets with knee-jerk attacks.