The last time President Trump claimed that “both sides” were responsible for bad behavior, it didn’t go well.

That was nearly a year ago, after a march of neo-Nazis descended into violence and a white supremacist drove his car into a crowd of peaceful protesters, killing a woman.

On Monday, Mr. Trump again engaged in immoral equivalence, this time during a gobsmacking news conference after his meeting in Helsinki, Finland, with the Russian president, Vladimir Putin. A reporter referred to last week’s indictments of 12 Russian military officials for a coordinated cyberattack on the 2016 election and asked Mr. Trump if he held Russia responsible. “I hold both countries responsible,” Mr. Trump said.

Even in a presidency replete with self-defeating moments for the United States, Mr. Trump’s comments on Monday, which were broadcast live around the world, stand out.