President Trump said Tuesday it would be “a little disappointing” if reports that the forthcoming Justice Department inspector general report concludes the FBI was justified in opening an investigation into his campaign in the runup to the 2016 election.

“The IG report is a very important report,” Mr. Trump said. “If what I read is correct, that will be a little disappointing, but it was just one aspect. We’ll see what happens. It is coming out in a few days. I hear it’s devastating.”

The Washington Post reported Monday that Attorney General William P. Barr disagrees with a purported portion of the report that found the FBI had a sufficient basis for launching its probe of the Trump campaign.

Mr. Trump said Mr. Barr may have been misquoted. The Post did not speak with Mr. Barr for the story but cited sources familiar with the matter.

“I have not seen the report. Perhaps he’s read the report. I think he’s quoted incorrectly,” Mr. Trump told reporters from London. “I do believe that because I’m hearing the report is very powerful, but I’m hearing that by reading lots of different things, not from inside information. It’s really from outside information.”

The president also hyped a separate report by John Durham, the U.S. attorney for Connecticut. Mr. Durham has been tasked by Mr. Barr to investigate the origins of the FBI’s Russia probe.

“I do think the big report to wait for is going to be the Durham report,” he told reporters. “That’s the one that people are really waiting for. He’s highly respected, and he’s worked very hard. He’s worked long hours, I can tell you, and gone all over the world.”