James R. Clapper Jr., former national intelligence director, questioned President Donald Trump's fitness for office following his freewheeling speech in Phoenix Tuesday night, which Clapper labeled "downright scary and disturbing."

"I really question his ability to be — his fitness to be — in this office," Clapper told CNN's Don Lemon early Wednesday morning. "I also am beginning to wonder about his motivation for it — maybe he is looking for a way out."

In Trump's remarks, delivered without a teleprompter, the president threatened to shut down the government over funding for the border wall he promised, opined that North American Free Trade Agreement will likely be terminated and hinted he might pardon former Arizona sheriff Joe Arpaio, convicted last month of criminal contempt.

Clapper said watching Trump's speech, he worried about the president's access to nuclear codes.

"In a fit of pique he decides to do something about Kim Jong Un, there's actually very little to stop him," Clapper said, referencing North Korea's leader. "The whole system is built to ensure rapid response if necessary. So there's very little in the way of controls over exercising a nuclear option, which is pretty damn scary."

Clapper has become a regular critic of Trump, who routinely disparaged the intelligence agencies during his campaign. But such a statement about a president by a lifelong military and intelligence professional — who has served at the highest levels of government under Republicans and Democrats alike — is extraordinary and perhaps unprecedented.

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Clapper, who said he has "toiled in one capacity or another" for every president from John F. Kennedy through Barack Obama, said Trump's Phoenix speech is the most disturbing performance he has ever watched. Clapper said the president should "have quit while he was ahead" after his speech on U.S. military strategy in Afghanistan. In that speech, the president read from a teleprompter.

In May, after Trump fired former FBI Director James Comey, Clapper said the country's core institutions were under assault from Trump.

"I think the Founding Fathers, in their genius, created a system of three co-equal branches of government and a built-in system of checks and balances," Clapper told CNN's Jake Tapper. "And I feel as though it's under assault and eroding."

The issue of Trump's fitness for the presidency has, until recently, mostly been raised by academics and partisan Democrats such as Hillary Clinton and House Minority Leader Nancy Pelosi, D-Calif.

In May, conservative New York Times columnist Ross Douthat, following revelations about Trump revealing classified information to Russian diplomats, suggested that the 25th Amendment be used, which provides for removal of a president who is "unable to discharge the powers and duties of his office ..."

Following the president's erratic responses to the deadly unrest in Charlottesville, the criticism came from his own side of the aisle, with Sen. Bob Corker, R-Tenn., questioning whether Trump has the "stability" and "competence" that are necessary to lead the country.

"The president has not yet been able to demonstrate the stability nor some of the competence that he needs to demonstrate in order to be successful," the senator told reporters in Tennessee last week. "And we need for him to be successful."