This is a big reason why it is unnerving to think about this man in the Oval Office:

Donald J. Trump’s unabashed and continuing hostility toward the parents of a slain Muslim American soldier, and his attacks on Republican leaders who have rebuked him for it, threaten to shatter his uneasy alliance with the Republican Party at the outset of the general election campaign.

Ignoring the pleas of his advisers and entreaties from party leaders in Washington, Mr. Trump only dug in further on Tuesday. He told a Virginia television station that he had no regrets about his clash with Khizr and Ghazala Khan, the parents of an Army captain killed in Iraq. And in an extraordinarily provocative interview with The Washington Post, Mr. Trump declined to endorse for re-election several Republicans who had criticized him, including the House speaker, Paul D. Ryan of Wisconsin, and Senator John McCain of Arizona, who both face primaries this month.

He also belittled Senator Kelly Ayotte of New Hampshire, who had criticized his treatment of the Khans, for not being supportive of his campaign.

For days, Mr. Trump’s top advisers and allies have urged him to move on from the feud, which erupted when Mr. Khan criticized him at the Democratic convention, and focus instead on the economy and the national security record of his Democratic opponent, Hillary Clinton. Yet, facing outcry on the left and right, Mr. Trump has insisted to associates that he has been treated unfairly by Mr. Khan, the news media and some Republicans, said people familiar with the campaign’s deliberations who insisted on anonymity to discuss them.

Whole thing here. 

Such is Donald Trump’s vanity and sense of grievance that he cannot help himself, even when his actions are demonstrably damaging his campaign — and even when the people closest to him are warning him to knock it off and get back on course criticizing Hillary. If he can’t stifle it for the sake of advancing his own political interests, how is he going to control himself when the national interests are at stake?

The other night, I had to have a talk with my 12-year-old son about not letting his emotions get the best of him when somebody or something makes him angry. He’s struggling with this, as adolescents do. I hope that by the time he’s 70, he’s mastered his passions — especially if he runs for president.

What happens when there’s an international crisis because some foreign leader insults Trump’s honor (such as it is)? A man with this kind of temperament in charge of the world’s biggest and most advanced fighting force is terrifying. If Khizr Khan and John McCain can get under his skin and into his head like that, how in the heck would he manage Hassan Rouhani and Kim Jong Un — to say nothing of Vladimir Putin and Xi Jinping?

This is not the behavior of a strong, mature man. This is the behavior of a weak, childish one. The Republicans ought to be steamrollering Hillary Clinton right about now. Instead, its nominee is defeating himself without Hillary having to lay a glove on him.