Just when Republican presidential candidate Donald Trump seemed to be pulling even with Democratic rival Hillary Clinton, he made a series of unforced errors that put him behind by 7 percent.

Trump went after the Muslim parents of a soldier who sacrificed his life for the United States and then ignored his advisors’ pleas to back off. Trump said he “always wanted to get the Purple Heart” and that receiving one from a veteran was “much easier” than being wounded in combat. He refused to endorse two prominent fellow Republicans—House Speaker Paul Ryan and Sen. John McCain—both of whom have endorsed him. Trump suddenly insisted that he had never met Russian president Vladimir Putin, contrary to earlier comments that he “got to know him very well” when they were on the TV program 60 Minutes together. He called on Russia to uncover Clinton’s emails, and suggested that he might recognize Russia’s claim on Crimea over Ukraine’s. He said he wanted to hit some of the Democratic Convention speakers “so hard their heads would spin.” And he described President Barack Obama as “the worst president, maybe in the history of our country,” even as Obama’s “Reaganesque” approval rating stood at more than 50 percent.

And that was just one week in the Trump campaign.

To err is human. To make unforced errors on a near-daily basis is Donald Trump. He has demonstrated time after time that his enormous ego compels him to respond to every slight with a jugular attack. His motto is: “Always get even. When somebody screws you, screw them back in spades.” A Trump presidency with this as its guiding principle would be a disaster for a world facing existential risks such as climate change and nuclear warfare.

A yuuuuge climate turnabout. When it comes to global warming, the divide between the two political parties is “the widest it has been in the decades since it emerged as a public policy matter,” noted an August 1 article in the New York Times. “That is all the more remarkable given that during the 2008 election, the Democratic and Republican positions on climate change were almost identical.”

In 2009, Trump signed an open letter to Obama and the US Congress that called for aggressive climate action and warned: “If we fail to act now, it is scientifically irrefutable that there will be catastrophic and irreversible consequences for humanity and our planet.” More recently, one of Trump’s companies cited “global warming and its effects” as justification for building a seawall around an Irish golf course. But if his political opponents see climate action as an urgent priority in 2016, Trump is against it.

Trump has said he would pull out of last year’s Paris Agreement, the historic accord that committed nations around the world to reducing greenhouse gas emissions. He intends to rescind the Clean Power Plan aimed at reducing emissions from US power plants. He has called for increased fossil fuel drilling and decreased environmental regulation. He even refers to global warming as a “hoax” invented by the Chinese. These are all unforced errors.

Trump is out of step with the American majority on climate change. A Gallup poll published in mid-March reported that “Americans are taking global warming more seriously than at any time in the past eight years,” with 64 percent worried about it. Two-thirds of Americans now blame human activity for rising temperatures and concern is rising rapidly among members of both political parties. Even Exxon Mobil is lobbying politicians and other energy companies to support a carbon tax.

What does Trump do when experts, political allies, and the general public disagree with his positions? He doubles down—saying, for example, that he has no regrets about his repeated jabs at Khizr and Ghazala Khan, the parents of the slain Muslim soldier. Trump is a man who could lead America off a climate cliff, insisting on the way down that he’s being viciously attacked.

The next decider-in-chief. Trump isn’t the only politician who makes unforced errors, of course. Clinton, for example, should have known better than to conduct State Department business on a private email server, or to explain her renewable energy program by acknowledging that “we’re going to put a lot of coal companies and coal miners out of business.” But if his track record is any indicator, a Trump presidency poses a far greater risk of civilization-threatening blunders. And when he gets in a hole, Trump just keeps digging.

Trump has said he would “tear up” the “disastrous” Iran nuclear deal—a deal that still faces many challenges but thus far is a success in many respects. Imagine what kind of unforced error Trump might make during a situation such as the 1962 Cuban Missile Crisis—in which the president has complete authority to order a nuclear strike. On his August 3 Morning Joe show, host Joe Scarborough claimed that, during a foreign policy briefing several months ago, “three times [Trump] asked at one point if we had [nuclear weapons] why can’t we use them.” (Trump’s campaign denied the story.)

And what about biological threats? Trump opposed Obama’s decision to send US troops to Africa to help combat the Ebola outbreak and said that American doctors treating the virus should be barred from returning home and “must suffer the consequences.” Until August 3, Trump was conspicuously silent on the Florida outbreak of mosquito-borne Zika virus—which can cause devastating birth defects—even while campaigning in the state and maintaining a residence there. The campaign’s vice chairman in Miami-Dade County said “we have bigger mosquitoes to squash” (such as building a wall along the Mexican border) and called Clinton’s campaign “sophomoric” for “taking on such an insignificant issue.” When Trump finally spoke out on the subject, he asserted that Zika appears to be “under control.” Another unforced error.

This isn’t just about the candidates’ positions on daunting issues. It’s also about the way candidates conduct their campaigns and handle missteps, revealing important clues about how they would govern.

Trump’s vanity, his shamelessness, and his unwillingness to listen to wise counsel give Americans no reason to believe that his unforced errors would come to an end before he could be installed in the Oval Office—indeed, the mistakes seem to be multiplying like mosquitoes in an old tire. If anyone other than Donald Trump had made this many unforced errors in one week, the Republican response would have been quick and sure: You’re fired.