At a news conference, Aug. 28, President Trump mistook one Finnish reporter for her colleague. He then responded to her question about how the U.S. would respond to Russia. (The Washington Post)

President Trump had successfully navigated Monday’s joint news conference with Finnish President Sauli Niinisto, a delicate affair that required him to balance just-completed diplomatic talks with the latest news about Hurricane Harvey, as well as public interest in his recent pardon of Joe Arpaio.

Then Trump started freelancing.

Joint news conferences with foreign leaders typically follow a short, rigid format: two questions for U.S. journalists and two for reporters from the home country of the president’s counterpart. Thirteen times before, Trump has adhered to this structure.

On Monday, however, Trump decided to keep rolling, after getting through the standard four inquiries.

“I know there might be a couple of more questions,” he said, turning to Niinisto. “Do you want to take one more? Would you want to take one more? Go ahead. Pick.”

A visibly surprised Niinisto obliged and gestured to a third Finnish journalist. “Please,” he said.

“Again?” said Trump, mistaking the woman for another female reporter who had asked a question earlier in the news conference. “You’re gonna give her — the same one?”

“No, she is not the same lady,” Niinistö replied. “They are sitting side by side.”

“We have a lot of blond women in Finland,” the reporter interjected.

True enough. And as presidential gaffes go, this was pretty minor.

Then again, it is always politically inadvisable to suggest that all (insert historically marginalized demographic group here) look the same. This principle certainly applies to Trump, a magnet for charges of sexism and racism.

Just a couple of months ago, during an Oval Office conference with reporters, Trump called an Irish female journalist over to his desk and told Ireland’s newly elected prime minister, who was on the phone, that the journalist “has a nice smile on her face. So, I bet she treats you well.”

That was an improvised moment, too — the kind that surely makes White House advisers cringe.

When Trump sticks to a plan, he can deliver a solid performance, as he did for most of Monday’s news conference. But when he ad-libs, he might suggest that a female reporter’s smile indicates soft coverage or reveals that he can’t be bothered to tell the difference between two women with the same hair color.