WASHINGTON — For a franchise as familiar with calamity as the Islanders, Monday affirmed that losses can still be as soul-crushing as ever.

The Islanders’ playoff fate fell out of their hands with a 5-2 blowout loss to the Capitals in which they were about as close to winning as Charlie Brown was to kicking the football.

The loss does not eliminate the Isles from playoff contention, but it does amount to an invitation for the Penguins to hop them in the standings.

“Disappointing,” said a despondent Casey Cizikas inside an Islanders locker room in which the preferred soundtrack was silence. “Just can’t happen.”

Pittsburgh, which did not play Monday, finishes its season with games against the bottom-feeding Blackhawks and Blue Jackets and now controls its own destiny.

So, too, do the Panthers, who moved a point ahead of the Islanders with an overtime loss to Toronto, but — in what somehow counted as optimism — lost on a John Tavares overtime winner, of all things.

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To make the playoffs, the Isles need to beat Montreal on Wednesday and hope that either the Penguins or Panthers lose.

Otherwise, add this game to the list of embarrassments with which the generation of Islanders fans too young to have seen the Dynasty is all too familiar.

Really, add the last 10 days, over which the Islanders have dropped three of five games in regulation to allow Florida and Pittsburgh the inside track to two wild-card spots. The Isles held pole position on them entering April.

The Capitals, who played without seven skaters including Alex Ovechkin and T.J. Oshie on Monday, scored their first goal, courtesy of Dylan Strome, within 36 seconds of puck drop and their second, courtesy of Rasmus Sandin, within 1:03. Shell-shocked and rattled, the Islanders would only recover enough to force Darcy Kuemper into a few acrobatic saves on a night where he finished with 38 total and easily outplayed Ilya Sorokin.

“Some errors were made,” coach Lane Lambert said, citing a lost faceoff, a defensive-zone giveaway and the Islanders tripping over their own sticks in the literal sense.

Asked whether there was enough urgency early in the game, Brock Nelson would say, “Probably not,” while Cizikas would say, “I don’t think so.”

“Obviously,” captain Anders Lee said, “a horrible start.”

The lack of intensity from the Islanders with their season on the line was nothing short of staggering.

Their defensive-zone play was something out of a blooper reel.

The forecheck never got going.

The power play, dysfunctional all season, was on for six minutes and recorded one shot on goal.

As they have so many times this season, the Islanders played down to an inferior opponent.

It is not just Monday but the accumulation of those games that could now cost them a playoff spot.

“Just gotta be ready,” Cizikas said. “It doesn’t matter if a team’s playing for their playoff lives or not. They’re coming out hard no matter what.”

Craig Smith added a third Capitals goal before the first period mercifully ended, getting the better of Sorokin on a blocker-side look after the Islanders again made a mess of things within the defensive zone.

“I don’t exactly know what caused the start,” Nelson said, “but that was the difference and now we need a little bit of help.”

Over the ensuing 47:47, the Islanders got their fair share of chances, but could not finish enough of them.

That included but was not limited to a Jean-Gabriel Pageau slap shot all alone in the slot, a three-on-one in which Pierre Engvall’s fumbled away a pass to Kyle Palmieri and a trio of Kuemper saves coming on Bo Horvat twice before the kicker on Anders Lee’s backhand.

By the time Hudson Fasching scored with 5:08 to go, it was only enough to set off a scrambling finish that included goals from Tom Wilson, Cizikas and Strome that proved only to inflate the final scoreline.

To lose a playoff spot now would represent nothing short of a calamity for an organization that believes itself to be within a window of contention — a belief that, if the Islanders miss the playoffs for the second straight season, would strain reality.

Last season, the Islanders could fall back on a series of disasters outside their control to explain away a disappointment.

This time around, there would be nowhere to look but the mirror for everyone in the organization..