Hillary Clinton trashed Donald Trump as completely incapable of serving as president of the United States while campaigning in Colorado on Wednesday.

Clinton took the stage and playfully noted that she likes fire marshals, which was a subtle jab at the GOP nominee. Trump criticized fire marshals for blocking access to his Colorado rally on Friday.

"There is no doubt in my mind that Donald Trump is unqualified to be president and unfit to be commander-in-chief," Clinton told the crowd. "Anyone who spends his time insulting our military, demeaning the service of our POWs and our fallen soldiers, insulting Gold Star families, this is not someone who understands the honor, the duty, of serving America."

She continued, "And it worries me, some of what I hear him say; I mean anyone who can be provoked by a tweet should not be anywhere near nuclear weapons."

Trump's running mate, Indiana Gov. Mike Pence, campaigned in Denver on Monday afternoon too and sought to counter her message. Colorado could become a battleground state and the Centennial State's nine electoral votes could play a critical role in November.

But a top Clinton super PAC reportedly cut its ad spending in Colorado for the next two weeks, as it has grown increasingly confident about its chances there.

Clinton sought to appeal to the state's millennial voters with a promise about how she intended to wipe away their student debt.

"Anybody with student debt, we're going to help you refinance the debt because in America, if Donald Trump can plead bankruptcy six times and refinance his debts, American students and families ought to be able to refinance their debts," Clinton said.

Clinton will continue campaigning out west and stump in Nevada on Thursday.