The Dodgers’ farm system has been headlined this year by a Big Four group of prospects, as ranked by MLB Pipeline: catcher Keibert Ruiz, shortstop/second baseman Gavin Lux, right-hander Dustin May and catcher/third baseman Will Smith.

The industry thinks of the quartet together, especially when wondering if Dodgers president of baseball operations Andrew Friedman would move any of the four at Wednesday's Trade Deadline. Recently, each member of the group has carved his own identity.

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Smith, 24, was recalled by the Dodgers on Friday and will be the team’s everyday catcher, according to manager Dave Roberts.

Lux, 21, has posted a gaudy 1.502 OPS through his first 21 games at Triple-A Oklahoma City and is poised to be called up to the Majors during the coming weeks.

May, 21, is the Dodgers’ top Minor League starter, averaging better than one strikeout per inning across Double-A Tulsa and Triple-A. He, too, could have a role with the Dodgers during the pennant race, as a power arm out of the bullpen.

Ruiz, 21, earned a recent promotion to Triple-A and has the unique distinction of accumulating more walks than strikeouts in this swing-and-miss season across baseball.

In many ways, the 2019 Trade Deadline -- and perhaps the 2019 Major League Baseball season -- will be defined by the Dodgers’ answer to the following question: After consecutive World Series defeats, will Friedman be willing to surrender at least one of the Big Four in order to address his team’s most obvious need: a shutdown late-inning left-hander?

Unfortunately for the Dodgers, dominant lefty relievers are in short supply on this year’s midseason trade market. Pirates closer Felipe Vázquez is the Dodgers’ first choice among possible bullpen acquisitions, sources say. While the price will be steep, one source said on Friday that the Pirates have spoken about Vazquez more extensively with the Dodgers than other suitors.

Sources say Pittsburgh is expected to seek a premium bat and premium arm in return for Vazquez, as if to atone for the departures of Austin Meadows and Tyler Glasnow in the Chris Archer trade a year ago. One industry source said the Pirates are likely to establish the asking price at May and Ruiz -- and perhaps one additional player -- in their talks with the Dodgers.

While one source expressed doubt on Friday that the Dodgers would give up both May and Ruiz for Vazquez, the left-hander’s long-term contract makes him particularly valuable to the Dodgers. Vazquez is signed affordably through 2021, with club options covering ’22 and ’23.

Ruiz is intriguing to the Pirates, who have had the worst production at catcher of any National League team this year. And if Smith demonstrates that he’s ready to catch full-time for the Dodgers, then Ruiz may be more attainable now than during the most recent offseason.

In other words, the Dodgers must determine whom they need more: a dominant left-handed reliever who eases the burden on closer Kenley Jansen or a switch-hitting catcher who may share time with Smith for the next six seasons.

And then there’s May, who represents another difficult decision: He could join the Dodgers’ rotation full-time next year, especially if Hyun-Jin Ryu and Rich Hill depart as free agents.

While there are no perfect acquisitions, Vazquez comes awfully close for the Dodgers. Their relievers are predominantly right-handed, meaning Vazquez would balance their bullpen in a way that right-handed trade possibilities Shane Greene and Alex Colomé do not.

Moreover, Jansen likely would be more receptive to sharing late-inning responsibilities with a left-hander, as opposed to a fellow righty. Jansen has thrown the most postseason innings of any reliever in the Majors since 2013. The Dodgers would like to manage his workload this October, especially if they encounter postseason opponents with a high percentage of left-handed hitters.

Nats (still) seeking relief

Nationals general manager Mike Rizzo is canvassing the Majors for late-inning relievers. Sources say he’s showing interest in Greene, Colome, Blue Jays closer Ken Giles and Blue Jays setup man Daniel Hudson, among others.

In many ways, it’s remarkable that the Nationals are Deadline buyers at all.

On May 24, the Nats awoke with the second-worst record in the National League after being swept by the Mets in a four-game series. Since then their 36-17 record is the best in the Majors, yet the bullpen remains a major issue. Even with the resurgence, Nats relievers have combined for the worst ERA in the Majors.

Closer Sean Doolittle is having a season in line with his career norms, but the lack of depth in front of him has been evident. Thursday’s loss to the Rockies was one glaring example, as 42-year-old Fernando Rodney -- the Majors’ oldest active player -- blew a save opportunity that fell to him because Doolittle had pitched both ends of a doubleheader the previous day.

Twins looking for a duo

The Twins are known to be looking for both a starter and reliever, and the possibility that they would address both needs in a single trade has been mentioned by those in the industry over the past several weeks. However, one source said on Friday that the team isn’t close to doing so.

If Minnesota revives the possibility, Toronto will be an ideal trade partner, because the Blue Jays could pair Marcus Stroman with Giles or Hudson. However, one source said the Twins aren’t inclined to offer both outfielder Trevor Larnach and right-hander Brusdar Graterol in an offer for Stroman and Giles.

It’s true: The Giants could buy

As the Giants’ remarkable return to relevance has continued, they’ve gone through multiple stages: First, they determined Madison Bumgarner was likely to stay, as first reported by MLB.com's Mark Feinsand. Then they started leaning toward keeping their relievers. Now they're looking like full-fledged buyers.

The latest proof? One source said on Friday that they’ve spoken with the Blue Jays about Eric Sogard, a free agent after this season.

One true test of a buyer is whether that team is willing to take on rental players. Against what were once considerable odds, the Giants are meeting that standard.