They've allowed more than 430 yards to each of their last three opponents, all with losing records. Starting with the third week of the season, they've been ranked as the worst team in yards passing and overall yards allowed.
And their secondary has been so weak and banged up that wide receivers Matthew Slater and Julian Edelman have played there a lot.
Somehow, the Patriots have won their last five games and are tied for the AFC's best record at 10-3. But can they continue winning with that shaky defense once the competition stiffens in the playoffs?
"It's always a concern when one running back gets over 100 yards," linebacker Dane Fletcher said Monday after the Patriots' 34-27 win at the Washington Redskins on Sunday. "It's getting (to be) crunch time here, so we've got to work on it."
The Patriots allowed Washington 463 yards, the eighth time in 13 games they've given up at least 427. Roy Helu rushed for 126 and Rex Grossman threw for 252 and two touchdowns. The journeyman quarterback even marched the Redskins from their 20-yard line with 6:30 left to the Patriots 5 with 1:15 to go.
That drive wouldn't have meant much if Brady hadn't thrown an interception in the end zone on the previous series when a field goal would have given the Patriots a 37-27 lead.
When he went to the sideline, Brady got into a shouting match with offensive coordinator Bill O'Brien. Backup quarterback Brian Hoyer stepped between them. When the game ended, Brady and O'Brien embraced.
"We're all held accountable," Brady said Monday on his weekly appearance on WEEI radio. "I'm glad our defense really made the play to win the game at the end, because I'd have been feeling pretty crappy if we'd somehow not pulled that game out with that interception there at the end."
He also said he and O'Brien have a "great relationship."
On the interception, cornerback Josh Wilson stepped in front of wide receiver Tiquan Underwood at the back of the end zone. Underwood was signed as a free agent on Nov. 8, cut on Nov. 12 and re-signed Nov. 24. In three games with the Patriots, he has two receptions.
The argument "is just part of the game. We're all passionate about our jobs," Underwood said.
He accepted blame for the interception.
"As a wide receiver, we run to get open and catch the ball," he said, "and if we can't catch it, no one catches it. So I have to just become a defender for Tom there and don't let the guy intercept the ball. It was a good play by (Wilson), but I know that I've got to run a better route to catch the ball and, if not, I have to bat it down."
Fortunately for the Patriots, they came up with the game-clinching interception six minutes later. It was the latest example of a bad defense playing well in the red zone.
They've allowed opponents inside their 20-yard line 52 times, tied for second most in the NFL. But they've given up touchdowns on just 50 percent of those possessions, 16th in the league. When 15 field goals are added in, teams have scored on 41 of those 52 possessions, a rate of 78.8 percent. And that's tied for fourth best in the NFL.
So how does a porous defense tighten up like that?
"The closer and closer you get to the goal line, the more it relies on attitude, the more you've got to rely on the guy next to you to keep them out of the end zone," Fletcher said. "In the field, it comes down to schemes and what they may or may not do, whereas on the goal line it mainly comes down to attitude and winning one-on-one battles."
The Redskins reached the red zone four times, scoring two touchdowns and a field goal before falling short at the end.
"We've tried to work hard on it," coach Bill Belichick said Monday. "There are still some things we can do better there."
They may have to on Sunday when they visit Tim Tebow and the Denver Broncos, who pulled out another late comeback win Sunday, 13-10 over the Chicago Bears. They're 7-1 with Tebow as the starting quarterback and came from behind in six of those wins.
"You have to give credit to how well the team's doing as opposed to one guy," Fletcher said, "because they're all stepping up."