Tanner Roark wipes away sweat as Cardinals first baseman Matt Adams circles the bases after a three-run homer. (Jonathan Newton/The Washington Post)

Max Scherzer fanned 13 New York Mets on Thursday night, bringing his season total to 290 and putting a “300-K watch” in place for his next start. The Washington Nationals right-hander, however, remains an underdog for the National League Cy Young Award because his 17 wins are merely a normal total and not comparable to Jacob deGrom’s 1.77 ERA — the 10th best in 50 years. DeGrom’s 9-9 record just indicts his Mets mates.

Unfortunately for the Nats, Scherzer’s starts are the only rock-solid pillar in their projected starting rotation next season. Everywhere else, there are question marks. That’s a huge problem because superb starters have defined the Nats’ era as contenders since 2012. In the years the Nats won the NL East, their rotations finished first, second, second and fourth in Major League Baseball in ERA. In 2013 and 2015, they slipped to seventh. This year, their starters’ ERA plummeted to 20th.

Fingers can be pointed in many directions. But that’s where you start.

Because General Manager Mike Rizzo says that a great rotation is always his central team-building goal, this constitutes a fundamental crisis. Remember, just three years ago, the Nats’ rotation was Scherzer; Jordan Zimmermann, then at his best; Stephen Strasburg; Gio Gonzalez; Doug Fister (off a 16-6 season); promising rookie Joe Ross; and, forced to the bullpen, Tanner Roark, who had won 15 games the previous year.

This year, the Nats have handed the ball to Tommy Milone, Jefry Rodriguez, Erick Fedde, A.J. Cole and Austin Voth, all with ERAs over 5.00, while being delighted to discover that off-the-scrapheap Jeremy Hellickson could go through a lineup twice before the Nats had to start wearing out relievers behind him.

Everywhere you look there’s reason to fret. Gonzalez, a seven-year stalwart, is gone. The injury-prone Strasburg has missed 32 starts — a full year’s worth — in the past four years. Roark has regressed to 22-26 with a below-MLB-average ERA of 4.50 for the past two seasons. And Ross, coming back from elbow surgery, has just 11 innings in the majors this season.

This rotation gulch cannot be allowed to waste another season because Scherzer and Strasburg, 30, are sure to be together only through 2021. The resources in free agent dollars that may be required to add a Patrick Corbin or a Dallas Keuchel — and perhaps another free agent starter, too — are just one more reason fans should take a long look at Bryce Harper in this final homestand.

Everyone in baseball knows the Nats have been tempted all season to let Harper drift away into free agency because they have a cheap and perhaps gifted outfield next season with Juan Soto, Adam Eaton and Victor Robles — total salary, $9.5 million. But another factor is pushing Harper out of town, too: all the money needed to fix so many other weaknesses at catcher, at second base, in setup relief and, above all, in that rotation.

Every team that falls out of contention looks to September as a time to find in-house answers to its problems. The Nats hoped they could, too. Instead, every area of need has shown weak, mediocre or indeterminate results this month. The Nats have waited for good news — even a two-week hot streak — to drop on them for months. Except for Soto and a couple of decent kid relievers, few have.

In September, catcher Matt Wieters has hit less badly but is still dead weight. Wilmer Difo keeps proving he’s a utility man, not a regular. After a torn Achilles’, how much second base can Howie Kendrick play next season? Wander Suero, Koda Glover and Justin Miller may be parts of a future bullpen but not back-end men on a contender. Even Robles, who hit a 427-foot homer in Miami on Tuesday, has looked overeager and raw in his few September opportunities, especially in game-on-the-line situations when he overswings.

What should bother the Nats most is that, behind Scherzer, Strasburg and perhaps Roark, who has had a good second half, the rotation is too much a mystery.

Ross’s return from Tommy John elbow surgery last year has been normal but not speedy. His paltry 37 innings this year, at all levels, will limit his innings next year. Behind him are Fedde and Rodriguez who, at 25, aren’t at “prospect age” any more. It’s time to show. In 17 starts between them, they have exhibited live arms and enough pitches but poor control and 100-pitch-in-five-innings inefficiency.

Even Manager Dave Martinez, the ultimate booster, gave Fedde a firm though friendly face-to-face talk in the dugout this week after he threw away a 4-0 lead by walking the leadoff man in the fourth, then the first two hitters in the fifth as he lasted only ­4 1/ innings. Rodriguez, currently pitching out of the bullpen, has had dominant moments, but no one can survive 35 walks in 50 innings. A crucial 11th-inning walk led to his loss Thursday to the Mets.

“The walks kill ’em,” Martinez said. “The other day with Fedde, it was the leadoff walks” with a four-run lead.

Some Nats fans hope the team could sign Harper, then trade Eaton, plus prospects, for a No. 3 starter. Even if they could, that adds only one player while costing $30 million a year or more for Harper, plus big money for that new pitcher. In that scenario, how do you fix your other needs?

You probably can’t because the Lerners have set their 2019 budget at about $180 million — the limit they deem as their norm in most seasons. It’s a figure that is market-appropriate to D.C. and should be enough. This year, their go-for-it payroll of more than $200 million was an anomaly that left them above the luxury tax ceiling. They want a “reset” next year to avoid future penalties. If Harper leaves, about $75 million in salary will disappear, promising an active winter.

As the Nats face playoff elimination, many think their big concern is how to try to keep Harper or cope if he leaves. If only their problems were so “small.”

Like many Scott Boras clients, Harper may not sign until after New Year’s. The Nats can’t wait that long. They have too many problems to watch as quality second basemen, relievers, catchers and, especially, starting pitchers get scratched off the list of significant free agents.

What do starting pitchers Corbin, Charlie Morton and J.A. Happ; catcher Wilson Ramos; reliever Craig Kimbrel; and second baseman Jed Lowrie have in common? They were all in Washington as all-stars two months ago, and they are all free agents this winter. So are 2017 all-stars Keuchel and second baseman DJ LeMahieu. How about relievers Jeurys Familia, Andrew Miller and Zach Britton?

The Nats face a scary but exhilarating offseason. Recently, Rizzo said the Nats had the proper young arms on their roster already to be a contender next year. I hope that nonsense is happy-talk misdirection. The Nats’ Job One is their rotation. Hunting season starts in seven weeks. Don’t come back until you bag your limit.

For more by Thomas Boswell, visit washingtonpost.com/boswell.