Longtime Washington Post editor and Watergate reporter Bob Woodward shared serious concerns about President Biden’s dismal debate performance — and likened the president’s fumbling to a “political hydrogen bomb.”

“I think the answer here is in reporting, in seeking very aggressively, an explanation — what happened here?” Woodward, 81, told MSNBC’s Air Melber on Friday.

Woodward said Biden’s debating was “so bad, so awful” that the American people had a right to know what was going on.

“We don’t want it to come out in some book or some memoir in a couple of years or a decade. We’d need to know now,” he insisted.

“I sat there and watched it and I could not believe it. I said, not only is this a political hydrogen bomb for him and the Democratic Party, it, you know — what happened? What happened?” the veteran journalist lamented.

Calls for Biden to step out of the race, Woodward explained, are now “inevitable.”

He speculated that the president may have been rattled by a “knock down, drag out fight” with his staff during debate prep.

Biden spoke with a noticeably soft, scratchy voice at the podium. Sources close to the White House insisted he had a cold.

While aides have already shot down the idea that Biden will consider dropping off the ticket, Woodward said that more energy should be put toward finding the source of Biden’s bad debate.

“Look, let’s step back. If a building blows up in downtown of some city, the story will be what happened and then the story will be how did this happen, why did this happen? And that’s where I’m very, very curious because this was a mega disaster,” he said.