Has Bill Belichick lost his mojo?

Richard Seymour has been everything the Oakland Raiders hoped he would be: a stalwart on the defense line, a leader in the locker room and a role model on the practice field. And despite being a week from his 32nd birthday, Seymour has begun this season — 10 tackles, 2.5 sacks and frequent double teams — the way he finished the last one, as a Pro Bowl caliber player.

In other words, Seymour is just the type of player the New England Patriots desperately need right now.

Nobody in the NFL has allowed more yards through three games than the Patriots, whose defense has deteriorated to the point where it could not hold a three-touchdown lead in Sunday’s loss to Buffalo.

The specter of Seymour, and what he once provided the Patriots before his trade on the eve of the 2009 season, will be ever present Sunday when New England visits Oakland.

And yet more haunting than the regret Seymour might rekindle is a stark truth: Bill Belichick has lost his mojo.

Belichick hasn’t lost his hoodie or his ability to drone non-answers in his press conferences, and he may well still be the best coach in the NFL. But he is no longer the difference maker, the savant who always seemed to be thinking two steps ahead of everyone else, which, in an era defined by parity, had set the Patriots apart.

No longer is The Patriot Way any different than the way of the Colts, Packers, Ravens and Steelers.

The Patriots haven’t won a Super Bowl since 2004, and they haven’t won a playoff game since 2007, and it’s not hard to see why.

The qualities that Belichick’s early Patriots teams were built on — shrewd scouting, disciplined players and smart coaching — are no longer so apparent.

In fact, the Patriots have become the type of team — with a great quarterback, a flashy offense and a defense that, as Bart Scott famously put it, couldn’t stop a nose bleed — the old Patriots would have scorned. If Tom Brady longed to be like Peyton Manning, this is not what he had in mind.

Most puzzling is that this transformation has taken place under Belichick, one of his era’s savviest defensive coaches. He masterminded two of the Super Bowl’s greatest defensive performances, when the Giants throttled Buffalo and the Patriots thwarted the Rams.

It is no small irony that the Patriots have been undone in the playoffs precisely the same way. First the Giants in the Super Bowl, and then the Ravens and Jets in the playoffs harassed Brady, ran the ball with conviction and were opportunistic throwing it.

Un-Patriot-like behavior manifested itself late in Sunday’s loss when defensive tackle Vince Wilfork earned an unsportsmanlike conduct penalty. It might not have prevented the Patriots from winning, but it prevented them from having a chance, allowing Buffalo to kick the winning field goal on the final play.

As for scouting, the Patriots’ drafts in recent years have been barren. They took 29 players from 2007-09 — players who should be the core of the team by now — but the only starters they have to show for it are linebacker Jerod Mayo and cornerback Patrick Chung. Among the busts was safety Brandon Meriweather, a former first-round pick who was cut after his bad behavior persisted.

The ballyhooed deals this summer, in which the Patriots acquired receiver Chad Ochocinco and defensive tackle Albert Haynesworth, smack less of bold ideas than desperation.

Ochocinco may be a productive receiver, but he’s never been a good route runner and the Patriots offense is predicated on precision. And it’s a surprise he is struggling?

As for Haynesworth, who hasn’t played more than 14 games since his rookie season, he was out (surprise!) against Buffalo with a back injury, which means he had only slightly less impact than he did the week before against San Diego when he was single-blocked and didn’t register a tackle.

Now, to be fair, the Patriots filched Wes Welker from Miami and have a pair of promising tight ends in Rob Gronkowski and Aaron Hernandez, and they did win 14 games last season, the NFL’s best regular season record.

But this is not how the Patriots are measured.

There is a different standard, which is why Belichick was lauded for dealing away Seymour in the last year of his contract and netting a first-round pick, which turned out to be rookie offensive tackle Nate Solder. Naturally, Belichick must have known something — Seymour’s backups were ready? He was ready to decline? — nobody else did.

It remains to be seen what kind of player Solder develops into, but what is clear is that during the prime of Brady’s career the Patriots miss Seymour more than Belichick thought they would.

Would Seymour have been the difference the last two years in the playoffs, and perhaps this one?

Who knows?

But what is becoming clear is that this deal, like some other Belichick decisions — the fake punt that backfired against the Jets in the playoffs, anyone? — is no longer an anomaly.

More often the sharpest guy in the room is only outsmarting himself.