JUPITER, Fla. — A.J. Cole has been on the cusp of making the Washington Nationals rotation for four seasons now. In 2015, he was up-and-coming. In 2016, he had a lot to learn. In 2017, he started to show consistency at the highest level. In 2018, he entered spring training as the favorite to be the Nationals’ fifth starter — and until the Nationals signed veteran Jeremy Hellickson on Friday, Cole was still the favorite to hold that role.

Cole doesn’t show much emotion, for better or worse. When asked about Hellickson’s arrival, he didn’t break character. But unlike the young player who was once deferential, Cole was noticeably firm.

“I’m going to do whatever they want me to do,” Cole said. “But I’m here for that fifth spot.”

At some point, even after years shuffling between Class AAA and the majors, even after years of being on the verge of steady major league duty but never quite securing it, young players seem to settle in to the major league clubhouse.

Cole is 26, no longer a young player. He is out of options and therefore must make the Opening Day roster or land on waivers, where another team could force him to start all over again. The Nationals just signed veteran Hellickson to challenge him for the fifth spot in the rotation. All of this, just when Cole was starting to seem like a player ready to stick.

Cole is quiet, soft-spoken and businesslike, an avid outdoorsman who grew up in Florida and never seemed affected by the bustle of big league life. When the clubhouse is full, his voice gets lost in the buzz. In this Nationals rotation loaded with elite talent, his stuff gets lost in conversations about Max Scherzer’s brilliance and Stephen Strasburg’s dominance and the rest.

But last season, Cole emerged as a reliable starter in a small late-season sample. General Manager Mike Rizzo always brings up Cole’s last seven starts as evidence of what he can do and to explain why the Nationals didn’t need to spend a fortune on a more established fifth-starter type. Cole averaged nearly six innings per start in those seven starts and pitched to an ERA of 4.23

“Last year, his last seven starts, he was really good,” Manager Dave Martinez said. “I just want him to keep building off that. We emphasized that to him … your last seven starts, you were a big league pitcher. Build on that.”

This year, he has emerged as more of a presence on the field and in the clubhouse and seems more determined to improve in the small ways that established players can focus on while those fighting for jobs wrestle with the big stuff.

When he plays catch, he talks pitching with anyone around, asking questions of Scherzer, Ryan Madson and others. He has taken his usual seat on the red chairs in the clubhouse and chatted pitching with catcher Matt Wieters, not just before starts but recapping them hours and days after.

“As I got up and was up there for that whole month [in 2017], I was able to get comfortable and settled in — learn the teams and the hitters,” Cole said. “It helps to get ahead of the hitters, get scouting reports and stuff on them instead of just getting thrown into a game.”

In the clubhouse, on the mound and even in the batter’s box, where he stood for the first time this spring Sunday, Cole looks stronger and more at ease than ever. Even though Erick Fedde has been pushing for a rotation spot all spring, and even though veteran Edwin Jackson seemed in competition for that role, Cole looked comfortable in his skin and confident in his position.

Then came Hellickson, out of the free agent bullpen, a veteran right-hander who multiple scouts agreed is not a clear upgrade over Cole, though he has shown the ability to keep hitters off-balance with a wide range of fastballs, an effective change-up and a curve. By virtue of experience alone, and the organization’s general affinity for proven veterans, Hellickson suddenly seemed likely to swoop in and steal that fifth spot.

But the Nationals have invested a great deal in Cole’s development and do not want to lose him. Rizzo, vice president of player development Bob Boone and special advisers to the general manager Dan Jennings and Bob Schaefer were in Jupiter on Sunday to see Cole’s penultimate spring training start. Rizzo and Boone sat a few yards from the pitcher’s mound, a few feet from the dugout, for their usual up-close view.

They watched Cole mix his low-90s fastball with an under-control curveball and inconsistent change-up mixed with sliders. They watched him work out of some trouble, surrender a homer on a 3-2 pitch to St. Louis outfielder Jose Martinez, but otherwise navigate a lineup full of Cardinals regulars without much trouble in a 10-0 loss that got out of hand after he left.

Between starts, Cole worked with pitching coach Derek Lilliquist, tweaking what he called his “hand angle,” something he felt helped him accumulate more swings and misses than usual as he struck out six Sunday in four innings. He only walked one. Cole hasn’t traditionally been much of a swing-and-miss guy in the big leagues, more a get-contact, get-outs type. Martinez said Cole’s two-seamer moved a great deal Sunday, another sign that his mechanics were in sync and his stuff was strong.

In other words, the Nationals’ decision-makers watched Cole turn in his best start of the spring at what basically amounted to the most pivotal moment of his career. Because for all the necessary rhetoric downplaying this week from his manager — “We told him to go out there and compete,” “We want A.J. to be A.J,” and the like — Cole had something to prove Sunday and will again Friday when he is scheduled to start one game of a split-squad set. Hellickson is scheduled to start the other.

The Nationals need a fifth starter April 4 at the latest, and though Hellickson has been throwing to hitters in California and threw 60 pitches over four simulated innings Saturday, he is behind Cole and the other Nationals starters in terms of workload.

But if the Nationals do decide to go with Hellickson, they will have to decide whether to move Cole to the bullpen or place him on waivers in the hopes he clears and lands in Class AAA Syracuse. Nationals evaluators like Cole and will not part with him easily. As of this weekend, all signs point to Cole sticking around, one way or another, though that might mean he has to serve as a long man in the bullpen while biding his time.

Right now, we’re looking at him as being a starter. The fifth starter. Here,” Martinez said. “ … We talked to him about it and we told him, ‘Hey, you’re going to be a big part of our success. Go out there and do your thing.’ ”

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