In New York, Attorney-General Eric Schneiderman​ revealed he had opened an investigation into the Donald J Trump Foundation "to make sure it's complying with the laws governing charities", based on troubling transactions that recently had come to light.

In Washington, the Justice Department was considering a request from Democratic members of the House Judiciary Committee to investigate a $US25,000 ($33,200) donation by the foundation to Florida Attorney-General Pam Bondi while she was considering, and subsequently decided not to, investigate alleged fraud at the controversial Trump University.

Such are the twists and turns on the campaign trail. With Democratic candidate Hillary Clinton staying home on doctor's orders, to recover from a bout of pneumonia that caused her to collapse on Sunday, the Trump campaign seemed even more energised than usual – with Clinton on her back, Trump could strut the national stage as he pleased, playing offence instead of defence.

He had a bit going for him – before Clinton faded she gave her "basket of deplorables" speech in New York and though she expressed regret for how she had dissed the GOP candidate's followers, Trump and his surrogates were pounding her.

More intriguingly, Clinton had stepped aside as some in her camp were sharing their worries with reporters – why wasn't she pulling ahead of Trump, whose campaign often is as unorthodox as it is cringeworthy?

Right now, analysts give Clinton an 80 per cent chance of winning the White House and her path through the Electoral College, which formally appoints the president, is way more secure than Trump's. But in the opinion polls that are grist to the mill of daily reporting on the campaign, Clinton is slipping.

In the aftermath of the party conventions in July, she had a commanding lead of almost eight points in the RealClearPolitics average of national polls. This week, that lead has tightened to just 2.4 points – so nail-bitingly within the margin of error for most polls that you might as well call it a dead heat.

All that's a worry – can't get out of bed; can't get ahead of the bloke she tells the world is a goose. And of huge tactical and strategic importance, the first of three head-to-head debates with Trump is just two weeks away, on September 26.

Some observers note that Trump has been uncharacteristically quiet about Clinton's health – but that's only because he doesn't have to say anything; her absence from the campaign speaks volumes. And over the last year, he and his surrogates had talked her into the grave – with every illness and frailty imaginable.

But just as the Clintonites worry, so too do Republican political professionals – such as pollster Robert Blizzard, who told The New York Times that it's too late for Trump to change voters' negative perceptions of him.

"Hillary Clinton clearly won the [northern] summer, and there's little doubt Donald Trump dug himself a very deep hole in the aftermath of the conventions [and] while he's starting to climb out of that hole now, his ability to take advantage of a few bad weeks for Clinton is going to be limited due to enduring views about his judgment, his temperament and his rhetoric towards other ethnicities and women."

But Trump adviser and retired general Michael Flynn was the eternal optimist, declaring that the campaign momentum had "totally shifted in Mr Trump's favour".

This was the week that Clinton was to make a series of speeches that she hoped would make the connection with voters who have so far eluded her. In campaigning, she might have successfully winged Trump; but to date she has been unable to take flight.

So the news of twin investigations of Trump's foundation offered timely relief for his rival. And in taking on Trump,  Schneiderman is no shrinking violet – after all, he's the guy who launched the Trump University fraud investigation that so riles Trump.

In June, Schneiderman told ABC's Good Morning America that Trump's real estate university venture was "really a fraud from beginning to end" and "just a scam".

And as news broke of the investigation into the Trump Foundation, a statement by the Trump campaign denounced Schneiderman as "a partisan hack who has turned a blind eye to the Clinton Foundation for years and has endorsed Hillary Clinton for president. This is nothing more than another left-wing hit job designed to distract from Crooked Hillary Clinton's disastrous week."

Obama's sweet talk about Trump was a brief self-reflection as he stumped for Clinton in Philadelphia.

Perhaps channelling a bit of that frustration over Clinton struggling in the polls, he pleaded: "Look, I understand. We're a young country. We are a restless country. We always like the new, shiny thing. I benefited from that when I was a candidate. And we take for granted sometimes what's steady and true. And Hillary Clinton's steady, and she is true."

And with that, Obama proceeded to demolish Trump – with shafts that were a mix of the serious and the jocular. He pinged Trump for posing as a friend of American workers and for being so friendly with Russian President Vladimir Putin: "Could you imagine Ronald Reagan idolising somebody like that?"

And then Obama rounded on the Donald J Trump Foundation: "[Trump] took money other people gave to his charity and then bought a six-foot-tall painting of himself – he had the taste not to go for the 10-foot version."