He pushed even harder. "Honestly, I don't think she's all there," Trump said on Sunday in New Hampshire. "She took a short-circuit in the brain," he added. He also called her "unstable," "unbalanced" and "totally unhinged".
And he tweeted this: Anybody whose mind "SHORT CIRCUITS" is not fit to be our president! Look up the word "BRAINWASHED."
Trump does this often. He'll be attacked for one thing or another and look to muddy the waters by arguing the same thing applies to someone else - usually Clinton. It's completely transparent in its simplicity and brazenness.
For example, poll after poll has shown the vast majority of Americans don't view Trump as being qualified to be president. Trump's response? Argue that Clinton isn't qualified.
In fact, the morning after Clinton herself said Trump isn't qualified on May 20, Trump basically said (to borrow another playground quote), "I am rubber and you are glue; whatever you say bounces off of me and sticks to you".
Trump tweeted: I said that Crooked Hillary Clinton is "not qualified" to be president because she has "very bad judgement" - Bernie said the same thing!
And he's kept up the attack ever since, tweeting: Hillary Clinton has bad judgment and is unfit to serve as President. https://t.co/3EzG620fpT
Polls also show the vast majority of Americans don't think Trump has the temperament to be president. A late May Washington Post-ABC News poll showed 70 per cent said Trump doesn't have the right kind of temperament to be president. Clinton has called Trump "temperamentally unfit" to be president.
So Trump now suggests it's Clinton who doesn't have the temperament - over and over.
"I have a winning temperament," he said last week. "She has a bad temperament. She's weak."
"She lacks the temperament," he said on Sunday.
"Hillary Clinton wants to be president," he said June 22. "But she doesn't have the temperament."
Trump has also endured months of attacks arguing that he and/or his policies are racist - particularly when it came to his comments about a judge of Mexican descent. So when Trump feuded with Senator Elizabeth Warren he said it was Warren who was the racist. Twice.
And after Democrats a couple of weeks back raised concerns about Trump receiving classified national security briefings, Trump responded the next day as you might expect, tweeting: "Hillary Clinton should not be given national security briefings in that she is a lose cannon with extraordinarily bad judgement & insticts."
Trump's effort in this regard has become completely transparent in recent days. But it's something that one person who has worked closely with Trump says he has long noticed.
Tony Schwartz, who ghostwrote Trump's The Art of the Deal and has been an extremely vocal Trump critic of late, tweeted a couple of weeks back that Trump's criticisms of others are usually more about himself:
"Something I saw early on w/ Trump: most negative things he says about others are actually describing him. Read his tweets with that in mind."
Schwartz re-upped the theory over the weekend, after Trump attacked Clinton's mental stability:
"Just listen to Donald Trump's eviscerating comments about Hillary today. He's talking about himself."
Schwartz also tweeted:
"Unhinged? Unbalanced? Not all there? Will cause destruction of our country? Who is Trump describing?"
Just listen to Donald Trump's eviscerating comments about Hillary today. He's talking about himself
The political strategy here makes sense - at least in theory. Trump is trying to turn his worst negatives into negatives for his opponent. If people don't think he's qualified to be president and doesn't have the temperament, the best way to mitigate the damage is to give people the same reservations about Clinton.
This is an old campaign strategy; Trump is just more shameless about it.
But the corollary to that rule is: If an attack doesn't fit into a pre-existing narrative, it's a tougher sell. "Crooked Hillary" builds on two decades of attacks on Clinton's character; a "Crazy Hillary" storyline does not. And unfortunately for Trump, it doesn't appear to be paying dividends. No matter how much he criticises Clinton's fitness for the job or her temperament, people just aren't buying it.
A new Washington Post-ABC News poll shows 60 per cent of people think Clinton is qualified to be president, versus 38 per cent who say the same of Trump. Similarly, 61 per cent say Clinton "has the kind of personality and temperament it takes to serve effectively as president," while just 31 per cent say that applies to Trump.
Her numbers on both of these questions are basically unchanged in recent months.
It seems this strategy works less well once you graduate beyond the playground.