There's a serious chance that Trump could still beat Clinton

Donald Trump
Carlo Allegri | Reuters
Donald Trump

There is a widespread belief that a Hillary Clinton presidency is a done deal.

Hillary Clinton supporters and a large portion of the mainstream news media have been convinced for months that Clinton simply cannot lose to Donald Trump under any circumstances. As a result, they see every twist and turn in this election as more proof that Clinton is succeeding and Trump is failing.

Here's a little World War II reminder of why that's a very dangerous mentality: In the weeks leading up to December 16, 1944, intelligence had been picking up evidence that the German army was planning a major counteroffensive in the Ardennes Forest. But the top generals in the Pentagon and in London dismissed the hard evidence right in front of them. You see, they had already determined and convinced themselves months before that Hitler's military machine didn't have any lethal attacks left in it. No amount of contradictory data were going to convince them otherwise. The result was what became known in the history books as "The Battle of the Bulge," a massive German offensive that caught the Allies by surprise and left 19,000 American troops dead and 56,000 more injured. It's also probably the most deadly example of confirmation bias in American history.

That groupthink mentality is also what led to the 2008 financial crisis that the U.S. economy is still struggling to dig out of. There was a widespread belief on Wall Street leading up to the housing market's collapse that subprime borrowers (i.e., people who might have trouble paying their mortgages) were a bottomless pit of growth and potential profits.

You and I now know how that turned out.

That sort of groupthink mentality about the inevitability of a Hillary Clinton presidency is in full force today. And it has already led to some serious errors.

"This smells like the elements of a nuclear-level trap confirmation bias. There's just no way this kind of self-assuredness at any point in a presidential election is warranted. Bigger — much bigger — deficits in the national polls have been overcome before in presidential elections."

Nowhere was this confirmation bias more evident than it was earlier this week as the Clinton team and much of the leading news pundits began pre-emptively dissecting Trump's visit to Mexico City and his subsequent speech on immigration policy in Phoenix. Their "conventional wisdom" was that the trip would fall flat and the immigration speech would simply feature more of the same rhetoric Trump opponents already pre-judge as racist bombast. Some slightly less brainwashed observers did grudgingly admit the Trump photo op with Mexican President Enrique Peña Nieto made Trump look more presidential. But they quickly joined the rest of the self-assured anti-Trump chorus when they bashed his immigration speech as a failure and insisted whatever good the optics of Trump's meeting with President Peña Nieto earned.

That was despite the fact that the speech really honed Trump's immigration message into a clear move against illegal immigrants with violent criminal records. And it's been breathtaking to see the contortions his opponents have subjected themselves to in order to convince themselves that trying to protect Americans from violent crime is somehow a bad message.

And of course, the recent Trump improvement in the polls isn't enough to shake them out of their religious-level reverie. Even poll guru Nate Silver has noticed the polls are tightening and the trend is favoring Trump, at least over the past few weeks. And more importantly, Silver has been correct in pointing out that if Trump does eventually overtake Clinton in the national popular vote it's very unlikely he will not do the same in the state-by-state electoral college battle.

Clinton's lead over Trump has narrowed to just over 4 points, according to the latest Real Clear Politics average of recent polls. In fact, two national polls (USC Dornsife/LA Times and Rasmussen Reports) actually shows Trump ahead.

But Team Clinton and most of the experts don't seem to think this means anything. Exhibit A: Clinton continues to lay low as if there's no way Trump could do anything she could ever need to counterattack with a major campaign appearance or event. And, the majority of the news media headlines and analysis about Trump focus on how he's an impossibly inept candidate with no support among mainstream Americans.

This smells like the elements of a nuclear-level trap confirmation bias. There's just no way this kind of self-assuredness at any point in a presidential election is warranted. Bigger — much bigger — deficits in the national polls have been overcome before in presidential elections. And with at least two national polls showing Trump actually now ahead, this would seem like a good time for everyone to reassess.

Interrupting your schedule to only to attend Tim Cook-hosted fundraisers and sending out well-produced but still nasty Tweets about Trump aren't the way to respond if your lead is narrowing. But hey, Clinton and probably everyone around her think she's got the election in the bag and they don't seem to care about much else.

Outside of the Clinton team, there's a more important audience that needs to get a better handle on the truth. That would be the American people, many of whom have only been told and are thus convinced that Clinton cannot lose. That mirrors the situation we saw earlier this summer in Britain, where the public was told daily by everyone from the political pundits to the gambling odds makers that the Brexit side would never win. Well, Brexit did win and the surprise outcome fueled a mostly unwarranted hysterical market reaction and national period of whining we could hear clear across the Atlantic.

The reaction to a Trump win in November would make the Brexit response look like a hiccup. Much of that surely loud and possibly violent response would be fueled by the surprise of it all. Anti-Trump Americans will feel a sense of betrayal by a news media and an overall establishment that didn't properly warn them of the outcome. It's time they started letting the public know there's a 50/50 chance this thing won't turn out their way.

Commentary by Jake Novak, senior columnist Follow him on Twitter @jakejakeny.

For more insight from CNBC contributors, follow @CNBCopinion on Twitter.