Cardinals shortstop Paul DeJong celebrates his game-winning home run in the ninth inning Monday night in St. Louis. (Jeff Curry/USA Today Sports)

Baseball’s consolation lies in its regularity, in the fact that every day demands new attention, and leaves little time for racing minds to stew about the day before. But the Washington Nationals are now a study in the downsides of that regularity, in the hopeless, demoralizing feeling that results from one faith-shaking loss after another.

Twenty-four hours after a walk-off grand slam turned hopes for a series win and a 4 ½-game deficit to dust, the Nationals suffered a loss nearly as agonizing to the Cardinals Monday night. They carried a two-run lead to the seventh, watched it become a two-run deficit in the eighth, stormed back in the ninth, only to lose, 7-6, when Paul DeJong homered against Koda Glover in the bottom of the inning.

They are seven games back in the National League East and have lost 21 one-run games. Baseball’s regularity is whacking them in the face now, serving daily reminders of the state of their depleted bullpen — and providing daily warnings that the playoffs are sliding further and further out of reach.

“I don’t know what else to do,” rookie manager Dave Martinez said after the game, referring to the plight of his struggling left-handed reliever Sammy Solis, who surrendered a three-run homer to Matt Carpenter in the bottom of the eighth that turned the Nationals’ one-run lead into a two-run deficit.

Martinez might as well have summed up the state of this team in general. What more can they do than hand a lead to their bullpen night after night? What more can they do than build leads on some of the best teams in the National League, undeterred by tough losses before them? What more can they do than give the ball to the relievers they have, when Shawn Kelley and Brandon Kintzler are gone and Sean Doolittle, Kelvin Herrera and Ryan Madson are hurt?

Nationals reliever Koda Glover walks off the field after Monday night’s loss. (Tom Gannam/Associated Press)

“You’ve just got to keep going,” Solis said. “There’s really no alternative.”

Solis inherited a one-out, one-on situation and a one-run lead in the bottom of the eighth inning. The lefty has struggled to get lefties out this season, so much so that the Nationals sent him to the minors for a stretch to figure it out. Solis gave up the tying two-run single in Friday’s loss to the Cubs, then allowed the eventual go-ahead run to reach before Martinez pulled him that day.

Monday, he allowed another single to put himself in a two-on, one-out jam. Then he tried to throw N.L. home run leader Matt Carpenter — a lefty — a high fastball, which is a pitch Carpenter doesn’t like, according to Matt Wieters. Solis missed low, a pitch Carpenter does like, according to Wieters and the swing he took sent it over the fence.

“He’s gotta get lefties out,” Martinez said. “ … I know it’s not easy, but that’s his job, and he hasn’t been able to do that.”

Martinez’s other left-handed option, Matt Grace, is less of a matchup type who lacks the blow-you-away stuff the Nationals see in Solis. Martinez also had to hold him in case Gio Gonzalez struggles Tuesday, something that has happened regularly, because Grace is one of the few relievers the Nationals have who can provide much length.

Juan Soto’s two-run homer had given the Nationals the lead back in the seventh inning. (Tom Gannam/Associated Press)

After Carpenter’s blow, the Nationals might have been broken after two days of late-inning agony. Instead, they rallied. Anthony Rendon, back in the lineup after missing two games, singled. Juan Soto, who homered to give the Nationals their two-run lead in the first place, walked. Daniel Murphy singled home Rendon. Wieters singled home Soto, at which point the Nationals had the tying run 90 feet away and two chances to bring it home. They could not do it. The game stayed tied, though only briefly.

Martinez chose Glover to pitch the ninth because he had no other options. Though Madson got treatment on his back problem Monday, he was not 100 percent certain he would feel better than he did in Sunday’s ninth inning debacle. Martinez decided he couldn’t risk it. Instead, he chose Glover, the most natural closer there. Glover tried to challenge DeJong. DeJong beat him.

“He definitely got my a--,” Glover said.

Glover should not be pitching the ninth inning in these games, not with the relievers on this team’s roster. But he is, and could be for the most important stretch of Washington’s season. Solis should not be the only option for lefties, but as of Monday, he was — though that could change if the Nationals decide to make a roster move Tuesday. And the Nationals should not be a game over .500 on August 14, seven games back in the division and all but out of the playoff race entirely. But here they are, with another game tomorrow, no relief help in sight, and very little choice about what to do next.

“Keep playing,” Martinez said. “ . . . Just keep playing baseball. That’s all I ask. This thing will turn around.”