240 years of democracy v. Trump: How he lit his last chance on fire

Trump on accepting results: I'll tell you at the time

Donald Trump had a final chance to stabilize his flagging campaign and make a play for the dwindling slice of undecided voters. He took that chance and set it on fire.

After a relatively strong start to the final debate of the 2016 campaign, Trump once again descended into unhinged conspiracy mongering, refusing to say if he would accept the outcome of the presidential election next month, an unprecedented rejection of American political norms.

"I will look at it at the time. I'm not looking at anything now, I'll look at it at the time. What I've seen, what I've seen, is so bad," Trump said Wednesday night before arguing that the media has "poisoned the minds" of the voters. He also cited a Pew study on voter roles that actually found no evidence of voter fraud, undermining his own case.

Pressed by moderator Chris Wallace, the GOP nominee once again demurred: "What I'm saying is that I will tell you at the time. I'll keep you in suspense, OK?"

Republican presidential nominee Donald Trump (C) walks off the stage surrounded his wife Melania Trump (L), his son Donald Jr (R) and other memebers of his family after the final presidential debate at the Thomas & Mack Center on the campus of the University of Las Vegas in Las Vegas, Nevada on October 19, 2016.
Robyn Beck | AFP | Getty Images

If you wanted to turn off undecided voters unhappy with Hillary Clinton but unsure of Trump's fitness to serve as president, you would be hard pressed to find a better way to do it than to suggest you won't accept the outcome if you lose.

Polls already show Trump lagging badly behind Clinton on the critical questions of having the judgment and temperament to be president. Trump's debate performance will only make these numbers worse. Voters mostly don't like Clinton but they see her as a safe choice for president. They see Trump as the opposite.

Trump surrogates spent the post-debate hours furiously spinning his election-rigging comments, not exactly a sign they thought the GOP nominee won the debate. Campaign manager Kellyanne Conway spent Thursday morning arguing that Trump meant he would not accept the results until they are certified.

"Why would he before he knows the results and they're verified and they're certified concede an election that didn't happen yet. That's insane," she said on CNBC's "Squawk Box."

She want on to cite Al Gore in 2000 as an example of refusing to pledge beforehand to accept an electoral outcome.

This is a specious comparison. Gore first conceded to George W. Bush on election night then retracted his concession as networks changed their call of Florida and instead said the race was too close to call. An automatic recount began in the state that would decide the election.

Gore and his legal team pursued the recount with vigor but when the Supreme Court stopped the recount and the Florida results became official, he immediately conceded despite protests from many in his party.

Trump would be well within his rights to refuse to concede on Nov. 8 if the outcome is in serious doubt and recounts are required. That is not what he said on Wednesday night. He suggested there was going to be massive voter fraud, that the press had rigged the election against him and that Clinton should not be "allowed" to run. Gore never did anything remotely resembling this.

Trump is irresponsibly and dangerously encouraging his supporters not to accept the outcome of an election it appears the GOP nominee will lose quite badly. As many editorial boards pointed out on Thursday morning, such comments are antithetical to a democracy that has rested for 240 years on the assumption of a peaceful transfer of power.

There were other shocking moments in the debate, including Trump's continued refusal to accept the fact that Russians are hacking the U.S. election in order to help him win. This is the unanimous consensus in the intelligence community. This is what Trump had to say: "She has no idea whether it is Russia, China or anybody else. ... Our country has no idea."

When Clinton accused Trump of being a "puppet" for Russian President Vladimir Putin, Trump's response was: "No puppet. You're the puppet." This is literally the "I know you are but what am I" defense more common among adolescents. Trump did not dispute that he used Chinese steel to build his Las Vegas hotel or that he has used undocumented immigrants on other projects and underpaid them.

And he suggested that it was Clinton's fault that he used the Chinese steel and that he has paid no federal income taxes for years. Scientific post-debate polls from CNN and YouGov showed Clinton won the debate by a comfortable margin. The GOP nominee had one final shot to convince Americans he would not be a dangerous embarrassment as president. He failed and is going to lose.

—Ben White is Politico's chief economic correspondent and a CNBC contributor. He also authors the daily tip sheet Politico Morning Money [politico.com/morningmoney]. Follow him on Twitter @morningmoneyben.