Jerry Blevins. (AP Photo/Lynne Sladky)

The Nationals’ bullpen has been among the best in baseball since the start of the season. Four months into the season, their 2.95 ERA is fifth best in baseball. But over the past month, their performance has slipped. They have a 4.87 ERA over the past month, worse than all but five teams. The past week has been particularly rough for them.

Over the past month, rookie Aaron Barrett, who is on pace to throw more than he ever has in his career in one season, has a 9.53 ERA. Craig Stammen, who pitched Thursday for the first time in eight days, has a 7.71 ERA. Jerry Blevins, who has struggled against right-handed batters, has a 6.48 ERA and Rafael Soriano, who had his season’s worst outing this week, has a 5.40 ERA.

“I don’t think they’re worn down,” Manager Matt Williams said. “I don’t think their innings are excessive or anything like that. It’s just a little rut. You can get out of those ruts quickly, as quickly as you can get in them.”

The Nationals bullpen has amassed 314 2/3 innings, the 10th smallest workload in baseball. Only one reliever — Stammen and his 54 1/3 innings — ranks in the top 50 in innings. Tyler Clippard has appeared in the most games, 48, among Nationals relievers but that’s still only tied for 34th most in baseball. Some of the relievers’ ruts are coinciding.

The Nationals explored the trade market for relievers and tried to make a deal but considered the asking price too high; they didn’t want to part with prospects such as Class AAA outfielder Steven Souza Jr. The Nationals wanted to upgrade their bullpen with, perhaps, in the back of their minds the memories of a worn down relief corp during the 2012 pennant race. Williams has been cautious recently of overusing certain relievers with large workloads.

The bullpen doesn’t have any glaring weaknesses but certain relievers have have endured certain struggles. Blevins has a 5.45 ERA but has held left-handed batters to a .145 average. Barrett’s performance has slipped of late. Soriano and Stammen have endured small rough patches in otherwise strong seasons. After a slow start, Ross Detwiler has pitched better recently.

The bullpen has held left-handed batters to a .237 average, the seventh lowest mark in baseball. It has held right-handers to a .249 average, the 14th best mark in baseball.

General Manager Mike Rizzo could always add a reliever in August via the waiver wire. He could even dip into the farm system to bolster the bullpen. Left-handed reliever Xavier Cedeno has bounced up and down this season several times already, and has held left-handers to a .156 average and right-handers to a .206 average at Syracuse. He has a 2.86 ERA in 25 games. Cedeno is already on the 40-man roster so he could be an easy addition, as is Taylor Hill.

But the Nationals don’t necessarily need a right-handed long reliever now (unless adding Hill as the long man frees up Stammen for more work as a multi-purpose reliever). Blake Treinen could do the same. Ryan Mattheus, who is also on the 40-man roster, has endured a rough season. He returned last week from an oblique injury but has a 4.94 ERA.

Left-hander Matt Grace, who was promoted to Syracuse this season, has a 1.05 ERA over 25 2/3 innings and has held left-handed batters to a minuscule .088 average. Right-handed reliever Rafael Martin, who has a great personal story, has yet to allow an earned run in 18 2/3 innings at Syracuse and has held right-handers to a .053 average. Right-handers Manny Delcarmen (2.98 ERA) and Warner Madrigal (2.87 ERA) have also had good seasons.