Why did he do it? Martinez's comments about Trump to an RGA crowd in April likely played a role. But, that doesn't explain Trump's broader tendencies in the 2016 race to attack candidates - Jeb Bush, Rand Paul and many others - long after they dropped out of the primary fight.
The real answer to the "why" of all of this is twofold: 1) Because Trump is a needler by nature and 2) Because he can.
For Trump, antagonism is second nature. It's how he engages with the world. Hit them before they hit you. Set the rules of combat first - and be willing to break them if necessary.
He views life - and politics - as a constant battle for respectability, authority, power, influence. That worldview is where "Little Marco," "low energy Jeb," "sleaze" reporters and a slew of other "very bad" and "dishonest" people comes from. You are either for or against Trump. There is no in between.
So, when a judge rules against him in a court case, the judge is bad and very corrupt. When a reporter writes a story Trump doesn't like or asks a question Trump doesn't approve of, the reporter is "very dishonest". When one of his rivals raises questions about his policies, that rival is a joke or a loser (or both).
Trump's life is a string of examples in which he has not only got away with this behaviour but seen it rewarded. He built his father's real estate company into a far larger and more profitable operation. He became a national and - gulp - international celebrity. He ran for president on a whim and wound up as the Republican presidential nominee.
He says and does what he wants because he can. Because it's always worked. And because, as he said, he just "doesn't care".
That sentiment is evidence of the often-overlooked aspirational quality to Trump's appeal for many voters. Trump is selling his version of the American Dream: Vote for me, be like me. While that idea prompts lots of eye-rolls in official Washington, it occasions lots of head-nodding at Trump rallies. Why? Because Trump is wealthy, married to a former model and can/does tell everyone what's on his mind at all times without any fear of retribution.
"He just doesn't care!," is something you hear often when you ask people why they like Trump. "He tells it like it is!" "He isn't politically correct!"
Trump's natural tendency towards antagonism and his "don't care" attitude would normally put him outside the political mainstream, dismissed as a loud-talking bully who doesn't grasp the gravity of the office he is seeking. In this election - where voters, especially on the Republican side - are willing to vote for anyone who can channel the rage and alienation they feel towards Washington, politicians and large institutions more generally, Trump has prospered.
Remarkable.
