The letter also says Trump has "none of the critical qualities" needed in a president, including discipline and the ability to control emotions, and he "lacks self control and acts impetuously". He also unveiled a new proposal to allow parents to fully deduct the average cost of child care from their taxable income, while insisting that when he's president, "Americanism, not globalism, will be our new credo".
"His tax plans would give super big tax breaks to large corporations and the really wealthy", Clinton said, characterizing the proposals, which include substantial tax cuts, as "trickle-down economics".
Trump chose Detroit as his backdrop, and his speech - though interrupted frequently by protesters - was clearly chosen to appeal to the working-class Americans who are at the center of his political strategy.
"A Trump administration will end this war on the American worker", he said, noting in particular that Obama's "anti-energy regulations" have destroyed millions of jobs.
The group also seems to question Trump's mental stability saying, "He is unable or unwilling to separate truth from falsehood", and "He lacks self-control and acts impetuously". Collins has the most moderate voting record of any Republican Senator, so it's not too surprising she'd join this group.
With Election Day exactly three months away, Clinton kicked off the week with campaign stops in the crucial battleground state of Florida.
Evan McMullin, a former Central Intelligence Agency official and a Republican, will file papers to run for president as an independent candidate. But McMullin could prove a complicating factor in the solidly Republican state of Utah.
It's an issue where Trump is polling even or ahead of Clinton, though she's gaining ground. Many are long-standing Trump critics, but the letter has some new names. A CNN Poll of Polls survey, meanwhile, put the former secretary of state 10 points ahead.
In the last few weeks Donald Trump has dug himself into a bit of a hole, insulting everyone from the Muslim-American parents of a fallen us soldier to GOP darling and House Speaker Paul Ryan.
Clinton is keeping the pressure on.
"The only issue now is whether Donald Trump is going to show up to debate at the date, times, places and formats set by the commission previous year through a bipartisan process", Podesta said.
In late July, Trump accused Democrats of trying to "rig" the timing of the debates by suggesting that they were scheduled adjacent to National Football League games happening in the fall. "It is reckless for a presidential candidate to publicly raise doubts about honoring treaty commitments with our allies". "Does he have the temperament to be president?"
I think he should release his taxes, Duffy told CNN's Wolf Blitzer on The Situation Room. "He has to do something that changes that dynamic".
Hillary Clinton is issuing a challenge to Donald Trump: I'm ready to debate.
The commission is led by both Republicans and Democrats.
Two Republican representatives, Virginia's Scott Rigell and New York's Richard Hanna, have publicly rejected Trump in the past week. One suspects that if Trump does claw back some much needed ground, then we should see traders react.