The linebackers couldn’t tackle Sunday. Zach Ertz dropped a sure TD pass. Fletcher Cox took a dumb penalty that cost the Eagles at least four points.

Most every player and coach had a hand in the embarrassing, 27-20 loss to division rival Washington. Jim Schwartz morphed into Jim Washburn. The Eagles rang up 114 penalty yards — mostly deserved.

But the biggest culprit wasn’t even in the stadium. Lane Johnson sat 1,350 miles away, presumably watching this monstrosity unfold on his family’s TV in Norman, Oklahoma.

The Eagles' right tackle began serving his 10-game suspension for a PED violation. One imagines what he thought, seeing his hapless replacement, rookie Halapoulivaati Vaitai, get rag-dolled by Washington’s front seven. We can only hope Johnson felt shame and guilt.

Vaitai was beat for a sack on the first play from scrimmage. And then again, four plays later. It quickly became clear that the fifth-round rookie was a prop in Washington pass rusher Ryan Kerrigan’s campaign to return to the Pro Bowl.

The Eagles offense was thrown out of synch. QB Carson Wentz had no time to set, and kept throwing high all afternoon. Plays were blown up before they could develop.

No one can fairly blame Vaitai for this debacle. The kid was drafted as a late-round project, barely played the preseason and didn’t even dress the first four games. Now he was dangled, figuratively naked, before one of football’s strongest, cleverest pass rushers. “Big V’ shriveled into “Little V.”

You wonder what Coach Doug Pederson was thinking. The decision to start Vaitai, rather than reconfigure the entire offensive line, had some logic. But when it became obvious early that the rookie was overmatched, Pederson needed to move to Plan B. He never did.

Pederson was asked afterward if he considered making changes to the line at halftime.

“I have so much confidence in all our guys,” he said. “That sends a bad message to our team.”

I’m not sure what message it sends to be so stubborn that your prized rookie QB takes five sacks and gets whacked all afternoon. And the coach’s misplaced confidence — he called Vaitai “a warrior“ — won’t help when the Eagles next face the Vikings, who lead the NFL in sacks.

So Pederson takes culpability for lacking in-game adjustments. He takes more for not being better prepared when he knew what was coming for a month.

But it all goes back to Lane Johnson. Much as he tried to blame everyone else, including his union, for the 10-game suspension, it all falls on him. He had better options for bulking up than ingesting a mystery potion from a jar. The smart move would be to only take supplements provided by team trainers.

Johnson was sloppy and sneaky and now sits on the couch until Game 15. Players of his caliber are tough to replace and the Eagles have no good alternatives. When injuries destroy a team’s season, that’s unfortunate but unavoidable. When one player’s stupidity threatens it, that’s something else entirely.