The Post Sports Live crew tries to pick a reason why the Nationals did not live up to the offseason expectations. (Post Sports Live/The Washington Post)

The last five games of the Washington Nationals’ 2013 baseball season will not matter. That became official on Monday night when the Nats lost — in an appropriately cruel twist — to the St. Louis Cardinals, while both the Pittsburgh Pirates and Cincinnati Reds were winning their games.

That reduced the Nats’ not-so-magic number to avoid missing the playoffs to zero. Another season gone. Another long winter ahead.

And now it can be said, with almost no doubt, that the decision to shut down Stephen Strasburg last September didn’t cost Washington one chance to win a World Series, it cost the team and the city two chances. Because if one thing is clear about the debacle that was this summer it is that it was set up by the disaster of last fall.

Mike Rizzo has done a remarkable job as general manager since Stan Kasten handed him control of the team in 2009. He has proven himself to be a wonderful talent evaluator and, for the most part, a cool customer when it comes to important decision-making.

But he blew it on Strasburg. This isn’t a second guess, it was a first guess more than a year ago when Rizzo first announced his intentions. Almost everyone in baseball outside of Washington thought Rizzo was making a mistake then — especially when the Nats emerged as a clear championship contender — and they believe it even more firmly now.

Anyone who doesn’t think that the Nats’ meltdown against the Cardinals in Game 5 of the division series last October didn’t directly affect the team this season simply hasn’t been paying attention. Rizzo lost confidence in closer Drew Storen that fateful night and spent $28 million to sign Rafael Soriano during the offseason.

Soriano was, at best, reasonably competent as a closer. In mid-August, at the climax of the Nats’ remarkable post all-star break downward spiral, he had blown six saves in 37 chances and his ERA was 3.68. Like the rest of the team, he improved once the season was, for all intents and purposes, over.

Beyond that, the Soriano signing caused issues in what had been one of baseball’s most close-knit clubhouses. Storen pitched so poorly for one lengthy stretch that he was sent to the minors, which upset the entire team — notably his close friend Tyler Clippard, who very publicly ripped management for mishandling his pal.

That was during the period when the Nats were stunningly bad and dysfunctional. Having limped to the all-star break with a mediocre 48-47 record, they were 6-13 the next three weeks, effectively ending their season. The 30-13 run between then and Monday night was largely meaningless: The Nats had gone from a team with great expectations to one with no expectations.

The signing of Soriano wasn’t the reason the Nats failed, it was merely a symptom of why they failed. Everyone in the organization was trying too hard to justify the Strasburg decision. All of them heard the critics who said Strasburg’s season should have been stretched out to include October — either by resting him after the all-star break, shortening his starts or allowing him to pitch perhaps 10 to 20 more innings with what appeared to be a healthy elbow.

Having blown up 2012, a year in which the team had baseball’s best regular season record, the Nats set out to make certain their Strasburg decision was justified by winning in 2013. That’s where Manager Davey Johnson’s “World Series or bust” proclamation came from. It is also where the team’s tight play for more than four months came from. How many nights did the Nats leave men in scoring position in crucial situations — especially late in games? That comes from squeezing the sawdust out of the bat when you know your team needs a hit.

The old baseball saying is that good players and good teams “try easier.” The Nats were trying much too hard — in every possible way — for most of the season. They had to prove that blowing up last season was the right thing to do because it was going to make the future brighter.

That may happen — some day. But it certainly didn’t happen this season. For all the Strasburg-babying, he still spent time on the disabled list (in June) and has started exactly one more game — 29 — than he did a year ago. His numbers are hardly eye-popping for a 25-year-old who should be coming into his prime: 7-9 record, 3.02 ERA, although his massive potential is still apparent on some nights.

Chances are he would have pitched as well — or better — if he had pitched last October. And would have been equally healthy.

The good news is that the Nats get to start fresh next February. They will have a new manager who won’t carry the baggage of “World Series or bust” or the clear disagreements that Johnson had with Rizzo, dating back to the Strasburg decision. Maybe Rizzo will deal Soriano, who has only one year left on his contract, during the offseason and restore Storen, who is still only 26, to the closer’s role. Maybe Bryce Harper can stay healthy all season. And, perhaps most important, there won’t be any more delusions that a 98-win season one year automatically translates into being a good team the next.

The Nats can do two things this offseason: They can claim they were done in by injuries (check the Braves’ or Dodgers’ injury lists for the year before buying that one) or bad luck or near misses or bad calls. Or they can look in the mirror collectively and say, “We blew it. Let’s start next spring as if we haven’t won anything that matters.”

Because, as of this moment, they haven’t. And the fault, sadly, lies within themselves.