Republican presidential candidate Donald Trump dines with North Charleston (S.C.) Mayor Keith Summey on Thursday. (Jabin Botsford/The Washington Post)

Donald Trump has a go-to response whenever someone asks whether the angry impulsiveness he displays on the campaign trail befits a U.S. president — whether voters should trust him with his “finger on the trigger,” as the question is often phrased.

He opposed the 2003 invasion of Iraq.

That’s always his answer. And it proves, according to Trump, that behind the bluster is a man of sober judgment who won’t rush the country into a war it will come to regret.

The problem with Trump’s logic is that, in 2002 — before the invasion — he actually said he favored going into Iraq. We learned this Thursday night when BuzzFeed’s Andrew Kaczynski dug up an old interview Trump gave to shock jock Howard Stern, of all people. 

In the interview, which took place on Sept. 11, 2002, Stern asked Trump directly if he was for invading Iraq.

“Yeah, I guess so,” Trump responded. “I wish the first time it was done correctly.”

This is a good get. It shows that, once again, Trump is selling revisionist history to his backers.

But it’s also probably unlikely to change the minds of many people. The GOP front-runner has said that he was against the invasion so many times over the course of months that it is cemented as truth for those who support him. Until Thursday night, there hadn't been much reason to doubt Trump's version of events, because there had been scant evidence to contradict him.

And even now, it's likely Trump backers will look at this comment and think, He was put on the spot and didn't give a strong answer; maybe he hadn't thought it through yet and maybe he came to oppose it later.

This what Trump does. He strategically picks claims that are difficult to fact-check. In this case, it took months for someone to find the interview with Stern, which — having been conducted outside the mainstream news media — was tucked away in a place that journalists wouldn’t immediately think to look.

BuzzFeed appears to have been on the case for a while. In September, after Trump said during a debate that he was the “only person up here that fought against going into Iraq,” Kaczynski wrote that “there’s no record of Donald Trump being against the Iraq War before it started.”

True enough. But finding “no record” isn’t the same as finding proof to the contrary, which BuzzFeed didn’t turn up until Thursday. Others have tried to fact-check Trump’s Iraq invasion opposition, too, but they always seemed to be groping around for a way to prove a negative — that the Manhattan billionaire didn’t state his anti-war position as “loud and clear” as he claims today.

Proving a negative is always difficult and often unconvincing. There’s always a chance that you’ll miss something.

That’s what happened in November when the media tried to debunk Trump’s assertion that “thousands” of Muslims in New Jersey celebrated the collapse of the World Trade Center on 9/11. The media was left to prove that something Trump says happened didn’t happen. Reporters did their best, but all Trump needed to vindicate himself among supporters was to turn up a few clips talking about small groups of celebrating Muslims.

It didn’t matter then that Trump’s original claim about 9/11 was a wild exaggeration. And it almost surely won’t matter now that his supposed opposition to the Iraq invasion appears to be revisionist history.