WASHINGTON — By the time the ninth inning rolled around on Tuesday night, Washington Nationals manager Blake Butera had yanked almost every lever at his disposal.Designated hitter José Tena was out in right field with a turquoise glove and a prayer. Former starter Mitchell Parker was pitching in a spot that demanded high-leverage experience. Of the nine men on the field, only James Wood and CJ Abrams were in the same spot they occupied in the first inning.It didn’t work. The Nationals folded and were eventually swept at home by the Miami Marlins, who capped the series Wednesday by handing out a 4-1 defeat.As Clayton Beeter put it, the Nationals may be back under .500 after the loss, but they were “way worse than that” last year. They are, in short, ahead of schedule.It is, accordingly, time to both recognize developmental progress and treat the back of the roster with a more discerning eye.“I think the big blocks of creating a place, an environment where guys want to get better every single day … we’re seeing that,” manager Blake Butera said. “It’s starting to set that foundation. Now it’s just about making small improvements every single day to keep getting better.”Each day of the three-game sweep against the Marlins highlighted a potential improvement.Monday: Bullpen needs lefties, Nats need to identify more of themThe Nationals’ ace, Cade Cavalli, was at 89 pitches. Their left-handed bulk arm, Andrew Alvarez, had been moved to the rotation. Parker, their other left-handed bulk arm, needed to be fresh to follow Miles Mikolas on Tuesday. The only left-handed pitcher available was Richard Lovelady.In other words, Butera was stuck.He went to Lovelady, hoping the Marlins countered with a right-handed hitter to create a better matchup for their right-handed relievers later in the game. Miami responded predictably, but Lovelady entered and allowed a game-tying homer on what he called “a terrible pitch.”This isn’t to pick on Lovelady specifically, but rather the Nationals’ predicament. They are short on left-handed arms, so much so that Lovelady also had to open (and throw 41 pitches) on Tuesday. Their need for left-handed relievers has never been so pressing.That is, the correct mix of left-handed relievers. So far this season, Washington’s left-handed relievers have the highest FIP in MLB, which means they have struggled in the facets supposedly under their control (walks, strikeouts and homers).Parker and Lovelady have their respective strengths, but it’s hard to compete with those metrics.While the Nats hope to spawn the next generation of high-leverage lefties in the coming years, president of baseball operations Paul Toboni has conceded it will probably take a while before the big-league club benefits from their changes to the pitching development.