The approach of Tuesday's non-waiver Trade Deadline gives all teams -- contenders, pretenders and wait-for-next-summers -- a chance to take stock of their entire organizations. Clubs on the rise, like the Braves, must determine how wide open their window of contention is. Clubs that are struggling, like the Mets, must pick and choose which pieces they want to commit to for the future.
While most general managers don't love the word "untouchable," the truth is all teams have players they'd rather not trade under virtually any circumstances. Usually, the reasons why seem obvious. But in some cases, players who appear to be franchise cornerstones make for interesting trade chips.
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Here is a look at all five National League East teams and their most untouchable players -- plus one from each club who could, in theory, be an interesting piece to deal.
Braves
Who is untouchable: Ozzie Albies
Why: There aren't many more exciting players than Albies, a 21-year-old who has already reached the 20-homer plateau and who, along with Freddie Freeman, should anchor the right side of Atlanta's infield for seasons to come. This is the exact type of franchise player the Braves have been trying to develop. They're not trading him now, for anything.
Who is not: Julio Teheran
Why: The longer the Braves stay in contention, the less likely a Teheran trade becomes. But if they decide they're still a year away from real, legitimate end-of-October-type stuff, dealing Teheran to one of several pitching-hungry teams could make sense. Guaranteed $11.2 million next season with a $12 million team option for 2020, Teheran is growing expensive. His career-high walk rate of 4.3 per nine innings is alarming. And the Braves don't necessarily need him, with a glut of young pitching on the way.

Marlins
Who is untouchable: Sandy Alcantara
Why: The Marlins didn't deal a franchise-type player in Marcell Ozuna only to flip the return half a year later. While a right axillary infection has prevented Alcantara from spending much time on the mound lately, he remains one of the highest-upside players in the Marlins' organization, with a fastball that rides into the upper 90s. Miami has reason to hope Alcantara can be a big part of its next winning team.
Who is not: Jose Urena
Why: Although Urena sports a 4.63 ERA, he is enjoying the best season of his career in terms of peripherals. The 26-year-old's strikeout rate is up and his walk rate is down, making him attractive to contenders. So why would a rebuilding Miami club deal him? Urena will be arbitration-eligible for the first time this offseason, meaning he's about to get expensive. Pitchers are fragile. If the Marlins feel they're more than a year or two away from contention, it would make sense for them to cash in now, while Urena's value is peaking.

Mets
Who is untouchable: Michael Conforto
Why: Despite a subpar season coming off major left shoulder surgery, Conforto remains one of the building blocks of the Mets' future -- and an ultra-important piece given the possibility that Yoenis Cespedes will miss a chunk of the 2019 season. The Mets also aren't trading Conforto when his value is nearing an all-time low. They need him to be a rock in their outfield for years to come.
Who is not: Amed Rosario
Why: This may seem contradictory, considering Rosario is younger than Conforto and came to the Mets even more highly touted. But unlike in the outfield, where New York has a dearth of upper-level prospects, the organization is rich in shortstops. Nineteen-year-old Andres Gimenez (ranked No. 1 in the Mets' farm system by MLB Pipeline) is already at Double-A Binghamton, with 17-year-old Ronny Mauricio (No. 7) in the pipeline behind him. If the Mets decide Rosario is not the long-term answer at short, they could trade him now while his potential is tantalizing.

Nationals
Who is untouchable: Juan Soto
Why: Here is the complete list of teenagers thriving in the big leagues: Soto. He's the only one, and the Nationals have him under team control for at least five more seasons. He'll make close to the Major League minimum for the next two of them. Taking economics into account, Soto may be the most valuable asset in the game today.
Who is not: Bryce Harper
Why: To be clear, the Nationals aren't trading Harper. Probably. But what if the Phillies and Braves continue to keep the Nats at arm's length in the NL East? What if it becomes clear over the next few days, or even the next few weeks during baseball's waiver trade period, that the Nats are going to spend October at home for the third time in six seasons? If it happens again, Washington could deal Harper elsewhere for a haul of prospects. The Nats could do it if they believe they won't re-sign Harper, or they could do it if they intend to sign him back anyway. Either way would strengthen them for the future.

Phillies
Who is untouchable: Aaron Nola
Why: Still just 25 years old, Nola has blossomed into one of the NL's best pitchers. With due respect to Jacob Arrieta, whom the Phillies signed to legitimize their rotation, Nola is the Phils' ace as they push toward their first postseason berth since 2011.
Who is not: J.P. Crawford
Why: One of baseball's top-ranked prospects entering the season, Crawford has missed much of it with a right forearm strain, struggling when healthy. Parting ways with him would mean selling low on a 23-year-old with oodles of potential. But the Phillies committed to fellow shortstop Scott Kingery, not Crawford, with a six-year deal this spring. Even they don't ultimately pursue Harper in free agency, the Phillies have options on the left side of their infield. Dealing Crawford is certainly something the Phils could discuss this offseason, if not now.