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It's taken five seasons, but consistently poor defense has finally seen the Washington Redskins part ways with failing coordinator Jim Haslett. The decision was a mutual one, according to Mike Jones of The Washington Post.

Haslett's long overdue exit creates a vacancy the Redskins are already trying to find ways to fill, per ESPN's Adam Schefter:

The team's search for its next defensive signal-caller should focus on the following four candidates:

Pepper Johnson, Defensive Line Coach, Buffalo Bills

Few candidates are more intriguing than Pepper Johnson. The long-time standout NFL linebacker will be well-known to Redskins fans.

He was a key member of the punishing New York Giants linebacker quartet that left Washington and the rest of the NFC East battered and bruised during the '80s and early '90s.

Johnson was taught the nuances of the 3-4 from then-Big Blue head coach Bill Parcells, a master of the front. But he learned the art of hybrid flexibility from Giants coordinator Bill Belichick.

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He used Johnson in a variety of ways back then. Johnson lined up at both inside and outside linebacker, as well as on the defensive line in certain fronts.

He then followed Belichick to the Cleveland Browns. In 1994, Johnson was the heartbeat of the league's stingiest scoring defense. As the middle linebacker in Cleveland's 4-3, Johnson functioned as Belichick's on-field signal-caller.

After a brief and successful stint back in the 3-4 with the New York Jets, Johnson hung up his cleats in 1999. He's been coaching ever since.

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He spent years on Belichick's staffs with the New England Patriots, coaching both the linebackers and the D-line. During that time, Belichick was always keen to keep Johnson around.

That pattern ended last offseason when the assistant left to join the Bills. Johnson indicated he wanted to get out from "under the shadow of Coach Belichick," per an interview on WGR 550's John Murphy show (h/t NESN.com reporter Doug Kyed).

That's a good sign of Johnson's ambition to progress his career, say perhaps to the coordinator level.

Just as encouraging is Johnson's fine work has continued even without the influence of Belichick. The Buffalo Bills' fourth-ranked defense was spearheaded by a rampaging front four that accounted for 39.5 of the team's NFL-best 54 sacks in 2014.

In particular, tackles Marcell Dareus and Kyle Williams really flourished. Johnson could perhaps coax the same from Washington's talented but underachieving pair Chris Baker and Jason Hatcher.

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Johnson has played in and coached versions of both the 3-4 and 4-3. He's scheme versatile and aggressive in his approach. Just as important, he's also flexible, having learned from Belichick the art of taking away an opponent's favorite plays, something Haslett rarely did.

Since Doug Marrone walked out on the Bills, Johnson's future is naturally uncertain. As a rising star in the assistant ranks, he should certainly be on the list of candidates to whom Washington offers an interview.

Vic Fangio, Defensive Coordinator, San Francisco 49ers

Fangio's future will be determined by the San Francisco 49ers' search for a new head coach. But if he doesn't get the job and the Redskins are prepared to wait, Washington should waste no time giving Fangio a call.

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He's one of the grand masters of the 3-4 defense, with deep ties in the zone-blitz philosophy. Fangio has also shown a willingness to modify his more aggressive instincts in favor of a simpler system if it lets his players thrive.

That's how it's been in San Francisco since Fangio took over the defense in 2011. He has relied on very few fronts and consistent coverage structures to help his core of talented athletes dominate.

He's alternated between base 3-4 and 4-2-5 nickel looks, while usually relying on zone coverage behind it. During its best years, that paired-down approach allowed linebackers such as Patrick Willis, NaVorro Bowman and Ahmad Brooks to simply run to the ball. It also meant Aldon Smith was free to concentrate on rushing the passer, along with a line led by pocket-collapsing end Justin Smith.

But Fangio is no conservative play-caller who's a slave to the basics. He loves a good cornerback blitz and will also mix in some Cover 1 robber looks in the secondary to lock up receivers and bait quarterbacks into turnovers.

Fangio also isn't afraid to move players around to create matchup nightmares for an offense. He's used veteran lineman Smith as a standing rusher at times this season. Fangio also loves his front-line pass-rushers to execute a host of stunts and games to fool blockers.

He coped with a myriad of injuries and absences this season and still produced a stout unit. Willis and Bowman missed significant time through injury, as did nose tackle Glenn Dorsey. Meanwhile, premier pass-rusher Smith sat out nine games suspended. And you thought Haslett had it bad.

Still, Fangio's D ranked 10th in points and fifth in yards.

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The future of this brilliant defensive mind will be determined by events in San Francisco. The Niners' bid to replace outgoing head coach Jim Harbaugh could include Fangio.

That's perhaps why the Redskins weren't cleared to interview Fangio, per Mike Jones of The Washington Post:

However, the 49ers could end up giving the vacant top job to Fangio's D-line coach, Jim Tomsula, according to Mercury News reporter Tim Kawakami.

It's difficult to believe Fangio would stick around after being passed over for one of his position coaches. He'd be a terrific hire in D.C.

Steve Spagnuolo, Secondary/Assistant Head Coach, Baltimore Ravens

Steve Spagnuolo may seem like a curve ball as a candidate, but there's plenty to recommend him as Haslett's replacement. First, he's a master of designing and calling fire-zone blitzes.

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That skill helped him mastermind the Giants' destruction of Tom Brady and the high-powered Patriots in Super Bowl 42. Spagnuolo then bombed out as head coach of the St. Louis Rams, before being run out of town after one season calling the defense for the New Orleans Saints in 2012.

But the man who learned from the late, great, legendary blitz guru Jim Johnson with the Philadelphia Eagles has repaired his reputation since joining the Baltimore Ravens.

Watch any Ravens game from this season (Week 12's win over the Saints is a great example) and you'll see Spagnuolo's fingerprints all over Baltimore's sack-happy defense. When the Ravens bring pressure they move players into unorthodox positions, overload sides and rush from multiple angles.

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Spagnuolo's time working with Ravens coordinator Dean Pees, himself a fine defensive mind, has given him a firm footing in the 3-4. A Spagnuolo defense is one guaranteed to feast on confused quarterbacks.

Eventually, he'll get another chance as a coordinator. The Redskins would be wise to offer it.

Wade Phillips

Hiring Wade Phillips as defensive coordinator would likely turn out to be the best decision this franchise has made in half a decade. It's one the team is already thankfully exploring.

A key mover in any bid to bring Phillips to Redskins Park will be A.J. Smith. The experienced team-builder has been given a bigger role in the front office, per ESPN reporter John Clayton.

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ESPN Redskins reporter John Keim has detailed how Smith could help land Phillips:

Don’t be surprised if Smith pushes hard for Wade Phillips as the defensive coordinator. Phillips was the San Diego Chargers’ defensive coordinator for three seasons when Smith was the general manager. Smith was a scout and then pro personnel director in Buffalo during Phillips' six seasons as defensive coordinator and then head coach. In San Diego, Phillips' defense ranked 11th, 13th and then seventh in points allowed per game. They were 18th, 13th and 10th in total yards. Doesn’t sound like there’s any doubt Phillips would want to return to coaching. Phillips' son, Wes, also serves as the Redskins’ tight ends coach.

Smith's process appears to have started already, according to NFL Media Insider Ian Rapoport:

Phillips stayed at home in 2014 after running the Houston Texans defense for three seasons. Phillips inherited a truly dreadful unit and instantly remade it into one of the league's best.

Brian T. Smith of the Houston Chronicle notes how Phillips' units ranked "second in yards allowed in 2011 and seventh the next two seasons." Those defenses propelled the Texans to the first two playoff berths in franchise history.

The beauty of hiring Phillips is he'd bring with him a recognizable system. A coherent scheme is something Haslett never had. But Phillips' defenses have always travelled a familiar way.

That way is an attacking, 1-gap version of the 3-4 front which is more like a 5-2 front. That number five is significant because it's the number of rushers Phillips sends after an offense on the vast majority of snaps.

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Phillips is all about pressure. His linemen attack instead of absorbing double teams. His outside linebackers rush the passer and very, very rarely drop into coverage.

With Phillips calling the plays, the possibilities for players such as Ryan Kerrigan and Hatcher are truly tantalizing. If Washington manages to coax the 67-year-old back to a sideline, you can stop worrying about this team's defense.

Phillips is the best choice, but any one of the candidates on this list represents a major upgrade over Haslett and would improve a talented but underachieving defense.

Johnson and Spagnuolo would reward a gamble, while Fangio has the credibility of long-term excellence and a mastery of the 3-4. Phillips also boasts those qualities but is armed with a scheme that would make stars of several players already on the roster.