Drew Storen, right, hasn’t allowed a run in his last 20 innings, the longest current streak in baseball. (Alex Brandon/Associated Press)

The baseball world assumes that Stephen Strasburg, Bryce Harper, Ryan Zimmerman or Jayson Werth will someday define the Nationals’ identity. That may be wrong. Winning teams do not evolve around discrete individuals as much as they coalesce around core groups, like a superior starting rotation or a scary heart of the order. Then synergies among a group of players add up to more than the sum of their parts.

In Washington, a dream rotation or a fearsome lineup is years in the future, if it arrives at all. But a truly dominant bullpen with six or even seven relievers with a combined ERA under 3.00 — loaded with power arms and coming at foes in waves, almost always fresh, all different in styles, all nasty — oh, that is possible.

In fact, with the arrival of Cole Kimball in Nationals Park the last two days, on top of 100-mphHenry Rodriguez three weeks ago, we may be seeing it right now. They join a remarkable relief group — the only core part of the Nats that is already exceptional.

The Nats talk about all their young players who may, someday, be superb at core roles, like Ian Desmond, Wilson Ramos, Danny Espinosa, Jordan Zimmermann or Roger Bernadina. But none have achieved it. While we weren’t looking, one may have arrived.

Drew Storen hasn’t allowed a run in his last 20 innings, the longest current streak in baseball, and, with the season one-fourth finished, his ERA for ’11 is now 0.40. He’s learned to command his fastball, making his devastating slider and curve more effective. No one stays anywhere near 0.40 for long. But Storen has discovered that, so far as a pro, he’s continuing to add velocity, endurance and more precise control every year.

On Tuesday, Storen reaches his one-year anniversary in the big leagues and his ERA in 74 games is 2.65 — lower than his buddy Strasburg’s 2.91 was last season in a comparable number of innings. Foes have hit and slugged lower against Storen, too.

Tyler Clippard struck out all six men he faced in a game earlier this month. With four outs of scoreless relief on Sunday he lowered his ERA to 1.80 and helped the Nats beat the Marlins, 8-4, to reach the 40-game mark of their season at 19-21.

In the last two days, Kimball and Rodriguez turned the Marlins inside out. Saturday, Rodriguez had Hanley Ramirez so knee-locked by his sliders that, Storen said, “he looked like ‘if I come out of this alive, I’m all right.’ ” Of course, the Marlins glimpsed Rodriguez last week in Florida in a kill-the-mascot wildman show. So, they were loose.

The more polished four-pitch Kimball is already so close to being trusted that he pitched a scoreless inning in a 1-0 duel in his big-league debut Saturday. The bumptious rookie, who showed up the first day of spring training at 5:15 a.m., said he arrived at Nationals Park at 6:30 a.m. because “I couldn’t get the plane to fly any faster.”

Then on Sunday Kimball let Storen, who’d already warmed up, get a day off by pitching a scoreless ninth inning. Kimball closed the show by throwing three straight fastballs past Emilio Bonifacio. “That’s what we need,” Storen said. If Kimball can work in some semi-tight situations, it can reduce Storen and Clippard’s worrisome workload.

In their time in Washington, Storen, Clippard (2.85 in 140 games) and left-handers Sean Burnett (3.03 in 124) and Doug Slaten (2.90 in 65) have already given the Nats four dependable late-inning relievers. For reference, most of the all-time top 10 save leaders had career ERAs in this range, like Trevor Hoffman (2.87), Lee Smith (3.03) and John Franco (2.89). The rare Mariano Rivera at 2.22 is a mutant.

Until he was hit on the elbow by a liner Sunday, which may cost him a couple of days, hulking Todd Coffey was in the power mix, too, with a 2.45 ERA. At AAA, Collin Balester, with 3.33 ERA in 20 relief games for the Nats, waits if he is needed.

If all this, topped by the emergence of Storen as a shutdown closer at age 23, seems remarkably sudden, that’s because it is. When General Manager Mike Rizzo took over 26 months ago, his bullpen was one of the worst in history. So, he torched ’em all.

“Our bullpen was in bad shape, to be kind,” said Rizzo, who traded for Burnett and Rodriguez, signed Coffey as an inexpensive free agent, got Slaten (whom he’d drafted in Arizona) off the waiver wire, drafted Storen with the 10th overall pick and oversaw the switch of Clippard, Kimball and Balester from starters to relievers. Rizzo even signed reliever Matt Capps, the team’s only ’10 all-star, then traded him for Ramos.

“I think a deep bullpen, where you can trust all seven guys, is the wave of the future,” Rizzo said. “You see it on almost all the good teams. If they have a lead in the seventh inning, the game is just about over . . . And they are mostly power arms.”

“Except for me, all these guys began as starters. So, they all know how to use [more] pitches,” Storen said. “We don’t have cookie-cutter guys. Our deliveries, our stuff, you never get the same kind of look.”

Burnett slings crossfire with his hat crooked. Slaten is tall with a sinker and good breaking ball. Clippard is a throw back with a rising fastball and wicked change-up, so he uses the top half of the strike zone as much as any pitcher in baseball. The result: tons of strikeouts and the occasional home run. “It all goes together,” he said. Very well.

And Kimball? “He’s just a pie thrower,” Storen said.

A pie-thrower? Storen demonstrates a stiff-arm delivery you’d use to heave a pie if you didn’t want it to slip out of your hand. “But they are really hard pies.”

Some throw pies. Others peas. What Nats relievers have in common, starting in ’10 but even more now with all arms on deck, is that whatever they throw, it seldom gets hit.