"A man you can bait with a tweet is not a man we can trust with nuclear weapons."

So just ask yourself: Do you really think Donald Trump have the temperament to be Commander-in-Chief? 

Donald Trump can't even handle the rough-and-tumble of a presidential campaign. 

He loses his cool at the slightest provocation. When he's gotten a tough question from a reporter. When he's challenged in a debate. When he sees a protester at a rally. 

Imagine, if you dare, imagine — imagine him in the Oval Office facing a real crisis. A man you can bait with a tweet is not a man we can trust with nuclear weapons. 

I can't put it any better than Jackie Kennedy did after the Cuban Missile Crisis. She said that what worried President Kennedy during that very dangerous time was that a war might be started – not by big men with self-control and restraint, but by little men – the ones moved by fear and pride.

As Donald Trump arrived in Phoenix late Wednesday, fresh from a visit to Mexico City’s presidential palace, he had in his hands a big immigration speech that omitted the usual line that Mexico would have to pay for his proposed wall along the U.S. southern border.

Just after landing, though, Mr. Trump discovered that Mexican President Enrique Peña Nieto had tweeted that he had told the Republican presidential nominee during their private meeting earlier that day that his country would refuse to pay for the wall.

Mr. Trump was peeved …

So Mr. Trump hurriedly inserted a new sentence in his immigration speech, and he soon boomed out from the podium his traditional declaration that the wall would be paid for by Mexico—adding, “They don’t know it yet but they’re going to pay for the wall.”

“I have to add back the line that Mexico will pay,” Mr. Trump said, according to the people with him, adding that he couldn’t let that tweet go unanswered.