WASHINGTON -- Before the Phillies signed Bryce Harper in February, general manager Matt Klentak said the organization had an “objectively excellent offseason.”

They might need another one to catch the best of the National League East in 2020.

The Phillies lost on Thursday to the Nationals at Nationals Park, 6-3, to fall below .500 (79-80) for the first time this season and clinch a fourth-place finish in the NL East behind the Braves, Nationals and Mets. The Phils need to sweep the Marlins in the final series of the season to finish with a winning record, and they need to win twice to finish .500. They find themselves in this predicament because they were swept in a five-game series for the first time since Aug. 3-5, 1979, when the Pirates swept them in Pittsburgh.

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The Phillies are 7-15 (.318) since Sept. 3, which is the third-worst record in the league in that span. They are 46-58 (.442) since May 29, when they were a season-high 11 games over .500.

“I don't think we expected it to go this way,” catcher Andrew Knapp said. “I think there's a lot of factors that go into that. Injuries and stuff where guys are being put in situations that they normally wouldn't be in if we had a lot of those bullpen arms. Who knows what would've happened? But yeah, I don't think we expected it to go this way.”

There are many reasons why this has happened, injuries being one of them. They have lost seven key relievers, Andrew McCutchen, Jake Arrieta and Corey Dickerson. Jay Bruce has been unable to play in the outfield for months because of an injured left elbow. They lost Odúbel Herrera to a season-ending suspension.

Those things add up. The costs are real.

“I think a fully healthy Philadelphia Phillies is an entirely different ballclub than we have right now,” manager Gabe Kapler said. “I don't think anybody can dispute that.”

But other teams have suffered injuries and had issues, too. They have overcome them. The Phillies miscalculated the strength of their rotation before the season started. They could have had free agent Mike Moustakas at relatively little cost at third base, but they did not consider him an upgrade over Maikel Franco. They chose to be conservative before the July 31 Trade Deadline because they did not believe they could win the World Series.

The combination of those things leaves some people wondering how wide the talent gap is between the Phillies and the Braves, Nationals and Mets. Then there is the fact that the Phils are slogging to another finish, which could cost Kapler and others their jobs. Philadelphia is a combined 18-35 (.340) the past two Septembers. It is the fourth-worst record in baseball for that month over the past two seasons.

“It's definitely not due to lack of effort,” Knapp said. “It's just kind of the way it's gone for us. Everyone's out there really grinding towards the end of the year and it's just, the ball hasn't gone our way.”

Phillies left-hander Jason Vargas allowed five runs (four earned) in just 4 1/3 innings on Thursday, but he got no help from right-hander Edgar Garcia. Vargas loaded the bases with one out in the fifth, when Garcia entered the game with the Nationals holding a 2-1 lead. Garcia walked Yan Gomes to score Anthony Rendon, and then Asdrúbal Cabrera scored on a wild pitch and Ryan Zimmerman scored on a passed ball to make it 5-1 in a flash. It seemed like a fitting way to end a 3-8 road trip.

Vargas finished 1-4 with a 5.37 ERA in 11 starts with the Phils, who made him one of their acquisitions before July 31.

“Mediocre,” he said of his 11-start stint.

The Phillies have a $2 million buyout on an $8 million club option on Vargas for 2020. If they want to catch the Braves and Nationals next season, the Phils might need to decline it and look for bigger upgrades.

They will need to fill holes elsewhere, too.

“I'd love to be back,” Vargas said. “Selfishly, of course, I want to come back. I feel like it is a special group and is just really a few pieces away from having a chance to win the last game of the year. And it would be nice to have another crack at that with these guys. Hopefully that happens, but it is a business and I understand what goes on. And baseball is going to keep going on.”