Nationals starter Tanner Roark wipes away the sweat after yielding a three-run homer to former teammate Matt Adams in the first inning of the Nats’ 7-6 loss to St. Louis. (Jonathan Newton/The Washington Post)

There are constant reminders, on the mound and at the plate, in the bullpen and in the restless stands, of how much this Washington Nationals season has dissolved.

And there was another in the visiting dugout Wednesday night, as Matt Adams strode to the plate, biceps filling the sleeves of his St. Louis Cardinals uniform, his bat sending two baseballs into the far reaches of the right-field stands at Nationals Park. Adams’s two home runs were the foundation of the Cardinals’ 7-6 win, in which the home team was behind early, shaky in the field and energetic in another late comeback that fell short.

Adams also hinted at what the Nationals (69-71) gave up when their subpar play led them to trade him, Daniel Murphy, reliever Ryan Madson and starting pitcher Gio Gonzalez by last Friday. Adams’s two home runs, both off starter Tanner Roark, helped the Cardinals (78-62) build a six-run lead by the fifth inning. That he was wearing a Nationals uniform at the start of August, back when there was still a chance of a playoff push, only made that sting more.

“The home runs have really killed us,” Manager Dave Martinez said, reflecting on this game and the Nationals’ past few weeks. “I look back, and we’re giving up way too many homers, way too many homers. We have to figure that out. We really do.”

After a troubling first half — with a 3-12 record and 4.87 ERA at the all-star break — Roark won five straight decisions and posted a 1.61 ERA from July 25 to Aug. 25. Then came a start against Milwaukee on Friday in which he gave up three home runs in six innings. Then came Wednesday, starting at the top of the first inning, as Roark yielded back-to-back singles before Adams roped the seventh pitch of the game beyond the wall in right.

Ryan Zimmerman is safe on a home plate slide in the seventh inning. The call was challenged by the Cardinals but was upheld. (Jonathan Newton/The Washington Post)

The Cardinals stayed on Roark in the second, and this time the Nationals’ defense let the right-hander down. After two quick outs, Cardinals pitcher Miles Mikolas (14-4) hit a chopper to third and Anthony Rendon double-pumped the throw, putting Mikolas on with an infield single. Five pitches after that, Matt Carpenter hit a deep flyball to left-center field and both Bryce Harper and Juan Soto gave chase.

Harper squinted into the deep blue sky, seemed to settle beneath the ball at the foot of the warning track, then sputtered backward as it landed at the base of the fence. Mikolas raced home. Carpenter pulled into second standing up. Roark, who should have twice been out of the inning, had five runs on his line by the third.

Two innings later, Roark (8-15) hung a first-pitch change-up that Adams crushed into the second deck above the Nationals’ bullpen. Roark had given up just three home runs in 53⅔ innings heading into his start Friday. He has now served up five in his past 11.

“It was two pitches that were hit; they were mistakes,” Roark said of Adams’s home runs, indicating that he believed the rest of his outing went well. “What are you going to do?”

The Nationals chipped at the Cardinals’ lead, starting with the arms and legs of outfield prospect Victor Robles. Robles, who made his major league debut last September, lined a pinch-hit single into left field for his first knock of 2018. Adam Eaton followed with a double into the right-center gap, and Robles kicked into crowd-stirring motion, his body blurring past second and third and bounding into home at blazing speed.

That jump-started the Nationals’ offense, which scored four times in the seventh and has refused to cave as the season has spiraled. Harper, Rendon and Soto loaded the bases. Ryan Zimmerman scored them all with a double, and Wilmer Difo singled Zimmerman in to get the Nationals within one run.

But the Nationals, despite getting the tying run to second in the bottom of the ninth, never got closer.

Some 600 miles away in Atlanta, the Braves had blown a six-run lead and lost to the Boston Red Sox. Farther south in Miami, the Philadelphia Phillies fell one run short of the last-place Marlins. In Washington, again, was another missed shot for the Nationals to gain a little ground, however pointless that may feel with 22 games left to play.

Since Aug. 16, a week before the Nationals traded Adams and Murphy, the Braves are 8-12 and the Phillies are 7-13. There was a window for the Nationals to climb back into the National League East race. There was a sliver of opportunity. And yet they are now 9-10 in that same stretch.

“We thought all along we had a chance to catch those teams,” Nationals General Manager Mike Rizzo said before the game. “If we played the way we were supposed to be playing that we’d have an opportunity to make this a race. And that’s frustrating that we haven’t put anything together. That we haven’t really pushed them to the limits that we thought we should.”

Instead, as another September night wound down, a late push was dashed by early miscues, by a few unexecuted pitches, by a former Nationals player hitting home runs for a contending team.