WEST PALM BEACH, Fla. — Every day, the Washington Nationals pitchers throw bullpen sessions here at spring training with five pitchers lined up on mounds that are eight feet apart. Over the years — or decades — reporters get a sense of the quality of the arms in a team’s entire organization by standing behind a chain-link fence only a couple of steps behind those mounds, walking up and down, watching pitch after pitch from the whole staff, seeing the movement, speed and location of every throw.

This spring, as you walk behind that fence, you may see more major league-quality arms than ever before — almost 20 of them. That doesn’t equal a great staff. You would rather have six Hall of Fame thoroughbreds and the rest donkeys. But it is proof of deep talent and lots of options as a season progresses.

The Nationals have 29 pitchers here, and those arms will be the key to their season. General Manager Mike Rizzo builds his teams around pitching. When the Nats have a dominant, deep staff, they win the National League East. Or that has been the case in 2012, 2014, 2016 and 2017. When they don’t, the season is one long aggravation. And by the end, somebody may get choked or a manager gets fired.

What the Nats have this year is three amazing starting pitchers — Max Scherzer, Stephen Strasburg and Patrick Corbin — plus one healthy elite closer, Sean Doolittle, and a former monster closer coming back from elbow surgery in Trevor Rosenthal. Behind that are more than a dozen almost interchangeable arms — some young, some old, some hard throws, some soft teasers. Yet all of them exist in that same netherworld of hurlers who might be quite good in 2019 and combine to make a remarkable staff. Or, a year from now, many of them may be holding on to their careers by their fingertips. All have ability; none are a lock.

The result probably will be a 12-man staff with at least 18 pitchers — a half-dozen of whom, at any one time, will be stashed in the minors or on the 10-day injured list. Rizzo and Manager Dave Martinez keep talking about how many of their pitchers have “options” to be sent back to the minors, which gives them “flexibility.”

When the New York Yankees talk about their bullpen, they never mention who has options or what marvelous flexibility they possess. They just say: “Aroldis Chapman, Dellin Betances, Zack Britton, Adam Ottavino, Jonathan Holder and Chad Green.” And you say, “Mama, those bad men just struck me out again.”

From week to week, the Nats will try to figure out which of their big league arms are effective and healthy and which need a rest, are a bit sore or are just getting shelled. It will be a delicate task for Martinez, their second-year manager. But the good news is that he really does have a lot of pretty good pitchers, not just cover-your-eyes problems.

Luckily for the Nats, with decent health, roughly 50 percent of all the innings will be pitched by their three best starters and two best relievers. If the other dozen-or-more guys figure out how to pitch to a combined 4.00 ERA in the other half of the innings, everybody will end up smiling with 90 or more wins.

Scherzer, who struck out 300 last year, Strasburg and $140 million free agent Corbin, who’s a tall, lanky, athletic southpaw, will get the ball whenever they can stand upright.

No team in baseball has a significantly better top three. MLB is now awash in stat projection sites that measure every aspect of a player’s career, including his likely decline with age and his chances of reverting to his career-long statistical mean. I find it almost alarming how close some sites, such as Depth Charts, are to my own best guesses. For instance, this trio is “projected” to go 40-27 this year in 92 starts with a collective ERA of 3.42 and a total WAR of 12.4.

For comparison, and remember that stat-crunching computers don’t know the names or the fame of the players they are analyzing, the next-highest WAR trio in the National League is the New York Mets’ Jacob deGrom, Noah Syndergaard and Zack Wheeler at 12.2.

In the NL East, the top three Philadelphia Phillies and Atlanta Braves starters project to total WARs of only 8.9 and 6.5. The Phillies know they need another big arm, perhaps free agent Dallas Keuchel. But Atlanta, and its know-nothing Liberty Media ownership, seems unaware that analytics predict its five-man rotation will not have anybody with an ERA under 4.00 as everybody regresses toward previous career performance.

The Los Angeles Dodgers and Chicago Cubs have better fourth through seventh starters than the Nats, but the Mets and Washington appear to be the best loaded for October, when your top three starters are inordinately important. If you get there.

The Nats will walk a tightrope after their top three. One year ago, Anibal Sanchez was coming off three awful career-threatening seasons (20-30, 5.67 ERA) in Detroit. Last year in Atlanta, with Kurt Suzuki’s help, he reinvented his pitch selection style — in other words, he changed “the book” on himself. In 24 starts, a 2.83 ERA. Can that be approached again at 35? Tough task. Hitters can read.

Jeremy Hellickson is a similar, even scarier tale. In his past five years, his ERA is 4.69. In 2017, he gave up 35 homers in 164 innings. But last season, seldom being allowed to work through a lineup a third time, he had a 3.45 ERA. He burned up plenty of relievers, but he usually survived. His moxie appeals to everybody. But when he throws in the same group with Scherzer, Corbin and Joe Ross, whose pitches sound like gunfire when they hit catchers’ gloves, Hellickson sounds as if he’s pitching into a pillow. Naturally, this means he’s the guy I’m rooting for.

Behind him, slightly, for the fifth spot, are Ross, who looks as if he could uproot tree stumps with one hand, and former first-round draft pick Erick Fedde, who has gained 20 (needed) pounds over the winter. Ross has had a long, slow road back from Tommy John surgery and hasn’t yet resembled his promising form from 2015-16, when he seemed like a future rotation fixture. He’s on an innings limit this year. What really matters is whether, in 2020 through 2022, he will be the Ross who, in the first 32 starts of his career, had a 3.52 ERA, a 12-10 record and a big future.

The Nats have at least six relievers they think can be useful pieces for several years. If only they could be sure. This year, we will find out a lot of baseball truth about the promising trio of 2018: Matt Grace (2.87 ERA in 56 games), Wander Suero (4-1, 3.59) and Justin Miller (7-1, 3.61). If they are really that solid, they’re found money. Also, Kyle Barraclough, Koda Glover and Tanner Rainey (acquired for Tanner Roark) are all hard throwers with control issues at times. Which will win, their walks or their strikeouts? Southpaw Sammy Solis will get one more chance to prove he can learn how to gets lefties out.

We will have months to sort them all out. If just one starter out of Sanchez, Hellickson, Ross and Fedde has a standout season, if just three of those seven relievers click this season to join Doolittle and Rosenthal in the bullpen, the Nats will have a summer of fun. If not . . .

A coach approached Rizzo, who spends every day leaning on that fence, watching as his pitchers throw to imaginary nonexistent hitters.

So-and-so really looks good, the coach said.

“Yeah?” Rizzo said. “Who’s up at the plate against him?” They chuckle.

That will change soon enough.

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