Michelle Obama may be the only person on Earth that Donald Trump won’t attack. But why?

Michelle Obama impressed members with a passionate speech as she endorsed Hillary Clinton's candidacy (Getty)

Last week, we found out that Donald Trump's wife, Melania Trump, is apparently a fan of Michelle Obama's. In explaining her inadvertent plagiarising of the first lady's 2008 convention speech, Melania Trump's speechwriter said, "A person she has always liked is Michelle Obama."

Is it possible that Melania Trump's husband agrees with her?

As I noted last week, it's not that unusual for prospective or actual first ladies to say nice things about one another. There is something of a kinship, it seems, and they don't often get involved in the political sniping.

But here's the thing: Obama has now delivered two speeches that were very tough on Donald Trump -- albeit without mentioning him by name in either. There was one in an early June commencement speech and now on Monday night at the Democratic National Convention. Trump's response to each one has been silence.

Update: Trump has now broken his silence -- to praise Obama. In an interview with the Hollywood Reporter, Trump says of the speech that clearly targeted him in all but name: "I thought her delivery was excellent. I thought she did a very good job. I liked her speech."

And indeed, despite Obama's status as a first lady many conservative Republicans love to hate, Trump doesn't appear to have ever really gone after her for anything, really.

That's surprising from a guy who is nothing if not fond of doing things to stir up the GOP base. This is also a guy, mind you, who doesn't take incoming political fire without responding in kind. "I'm a counter-puncher," he has said repeatedly during this campaign. It's his explanation for many of his feuds.

It's also not as though he's opposed to engaging in political fights with women. Rosie O'Donnell, Megyn Kelly, Carly Fiorina, Elizabeth Warren -- the list goes on and on. And we all know how Trump feels about Obama's husband.

And yet, even as he tweetstormed during the big speeches of the convention Monday night -- especially during speeches by Warren, Cory Booker and Bernie Sanders -- not a word about the first lady, even as she made a very forceful case against him in no uncertain terms.

"I want someone with the proven strength to persevere," she said. "Someone who knows this job and takes it seriously. Someone who understands that the issues a president faces are not black and white and cannot be boiled down to 140 characters. Because when you have the nuclear codes at your fingertips and the military in your command, you can't make snap decisions. You can't have a thin skin or a tendency to lash out. You need to be steady, and measured, and well-informed."

It didn't escape notice:

"Donald Trump ranted about all the DNC speakers on Twitter -- except one," Business Insider said.

"There's One Person Donald Trump Did Not Try to Mess With Last Night: Michelle Obama," Slate said.

Some indeed painted it as Trump not wanting to pick a fight with a powerful and eloquent first lady who gave a fantastic speech.

But Trump's feuds are never quite so calculated. If he doesn't worry about "counter-punching" with Pope Francis -- the pope! -- why would he shy away from doing the same with Obama? This is not a guy who knows how to just let something go or can be prevailed upon to avoid an unhelpful political feud.

There is something about the first lady, it seems, that's different for Trump. And looking back, it's not clear that he has ever really targeted her in a forceful way.

In fact, four years ago at this very juncture in the presidential process, Trump actually praised her Democratic National Convention speech.

The year 2012 was not back when Trump was a Democrat, mind you. This was after he spent years questioning whether Obama's husband was born in the United States and was a legitimate president. His other tweets during that year's Democratic convention weren't nearly so kind.

And yet, praise for Michelle Obama.

Earlier that year, Trump did take a little dig at the first lady.

But that appears to be about the worst thing he's said about her. Other tweets mentioning her include asking what people thought of her haircut.

And he complimented her and her husband on their 20th anniversary in 2012.

Trump has always been a fan of stirring up controversy and appealing to the GOP base's antipathy toward everything Obama -- except, apparently, for Michelle Obama. Not yet, anyway.

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