Now, it’s all on Coach Mike Shanahan. The Washington Redskins’ leader must do just that — lead. With the team unraveling and the person in charge needing to pull it together quickly, we’re about to find out whether Shanahan is up to the challenge.

And after his poor performance Sunday in Buffalo’s 23-0 blowout victory here, the job may be too big for Shanahan. Perhaps this whole thing isn’t a good fit. The task may not be right for Shanahan at this stage of his career.

The question is fair following one of Washington’s most pathetic displays in recent memory. Things have been trending this way for weeks.

Dominated by the Bills from the outset, the Redskins dropped their third straight. Washington has lost four of its past five games. The 3-1 start? It’s only a memory now, fading faster each second during a once-promising season that could be careering toward a familiar, ugly finish. Unless the Redskins come together and get it fixed, there probably aren’t many victories left on their schedule.

Pass protection, run blocking, tackling, pass coverage — the Redskins failed at it all. No reasonable person should have expected the Redskins to emerge as one of the NFL’s top teams this season. Another embarrassing free fall, though, is simply unacceptable when even Shanahan says Washington improved during the offseason.

We’ve seen similar horror shows before. This decade, it has been a recurring, unsettling sight. Owner Daniel Snyder could have kept Jim Zorn for this, and saved a whole lot of money.

Outcoached from the start Sunday at Rogers Centre by his Bills counterpart, Chan Gailey, Shanahan had no answers during the game or afterward. “It’s a tough one to take,” he said.

For the first time in his career as a head coach or assistant, Shanahan said he was part of an offense that didn’t score. Obviously, the offense was awful, producing only 178 total net yards. The total included 26 yards rushing, with a 2.2-yard average.

The defense also continued to do its part.

Shanahan decided he needed to help defensive coordinator Jim Haslett after Washington gave up 829 yards in consecutive losses to Philadelphia and Carolina. He spent more time working with the defense in practice — and the Bills still produced 390 yards.

Buffalo quarterback Ryan Fitzpatrick had a 116.4 passer rating. Running back Fred Jackson rushed for 120 yards, with a 4.6-yard average.

And there was confusion in the Redskins’ secondary. So much, in fact, that inside linebacker London Fletcher lost it during the third quarter.

A blown coverage resulted in the Bills taking a 20-0 lead on a 15-yard touchdown pass from Fitzpatrick to tight end Scott Chandler. Following the play, Fletcher was shown on television shouting at a teammate who wasn’t in the camera’s view. Strong safety LaRon Landry said Fletcher was upset at him.

Cornerback DeAngelo Hall played peacemaker, trying to console Washington’s defensive captain. “It happens in the emotion of a football game,” Shanahan said. “Especially when there’s a missed assignment.”

This was a well-prepared football team? “No question about it,” Shanahan said.

Maybe Mike and his son, Kyle, Washington’s offensive coordinator, made halftime adjustments. If so, they weren’t apparent.

On offense and defense, Gailey and his staff had the Bills ready to roll. Shanahan and his guys needed to deliver creative counterpunches on offense and be rock-solid in their execution on defense. None of that happened.

Shanahan’s coaching couldn’t have overcome everything that went wrong against the Bills. But he delivered nothing. With the Redskins desperately seeking a spark — anything — the Great Innovator had no solution.

Were the Shanahans just hoping their beloved system eventually would succeed? They’ve been waiting on it since they arrived at Redskins Park.

Washington’s pass protection was awful. Often, it was nonexistent. Buffalo entered the game last in the league with four sacks. By halftime, the Bills had doubled their season total. They finished with nine.

Several key performers on Washington’s offense are injured, including two starting linemen. Injuries alone, however, do not explain the level of ineptitude on display from the Redskins for the entire game. Or what has occurred the past three.

Also, let’s be clear about this: The injured Redskins aren’t that good. They’re important to Washington’s offensive scheme. But the guys the Redskins lost weren’t headed to the Pro Bowl this season.

Washington’s offensive line was significantly better in the Week 7 loss to Carolina. Regression of this kind, in only one week, has nothing to do with the team’s talent level. This was about coaching. That’s Shanahan’s department.

“That’s a good question,” Shanahan said in response to a query about whatever it was the offensive line was attempting to do against the Bills. “It’s a disappointment.”

In his second start for Washington, quarterback John Beck had no chance. At halftime, the Redskins trailed, 13-0. Game over. It was as clear as Shanahan’s rotten judgment in picking Redskins quarterbacks. I doubt there are many quarterbacks who would have been effective Sunday behind the Redskins’ line.

Beck is trying to establish himself in bad working conditions. That’s a tough break.

During those rare moments when things went as planned, however, Beck didn’t do anything extraordinary. In his first start since the 2007 season, last week against Carolina, the inexperienced 30-year-old did some good things in the second half.

Problem is, the Redskins’ offensive line probably won’t be much better at any point this season.

Even when left tackle Trent Williams returns, the unit has major limitations. With that backdrop, it could be very difficult for the Shanahans to evaluate Beck. They can’t waste any more time tinkering with the game’s most important position.

Reality is, neither Beck nor Grossman is the short- or long-term answer at quarterback. In a perfect world, the offensive line would do its job well enough to help the Shanahans determine whether Beck could provide a bridge to Washington’s next quarterback of the future, wherever he is at the moment.

Mike and Kyle no longer have that luxury. They’ll have to ride it out with Beck for the remainder of the season (with Grossman as the other option, that’s the only smart move), and then bring in at least two new quarterbacks for next season.

In their second year under Shanahan, the Redskins shouldn’t be in such a mess. Something needs to change. Shanahan must prove he’s capable of fixing this — or step aside for someone who can.