LOS ANGELES -- Check the telephone poles in the Twin Cities on Friday morning. You might see signs that read:

MISSING: The Vikings' once dominant defense.

LAST SEEN: First half of the NFC divisional playoffs.

IF FOUND, PLEASE RETURN TO: A team hanging on to its championship aspirations.

The Minnesota Vikings' defense is in the midst of an identity crisis. Four games into the season, after a 38-31 loss to the Los Angeles Rams on Thursday night, what had been the backbone of this team has morphed into its Achilles' heel.

Where did coach Mike Zimmer’s vaunted scheme go, the one that ranked first in points and yards allowed per game in 2017 and recorded a historic third-down conversion rate at 25.2 percent?

Where did one of the most feared defensive units run off to? It was replaced by a group that allowed opposing quarterbacks to run or throw for three touchdowns combined in the first half in back-to-back weeks (Josh Allen two rushing TDs, one passing TD; Jared Goff four passing TDs).

The Vikings were dismantled by Rams coach Sean McVay’s play designs in situations where pass-catchers were once again left wide open for major gains or with a mismatch they could easily exploit. Somehow, linebacker Anthony Barr managed to be lined up against receivers that quickly took advantage of the discrepancy. According to NFL Next Gen Stats, Barr was the nearest defender on three of the Rams' passing touchdowns: the 8-yard TD to Todd Gurley II (1.71 yards of separation), the 70-yard TD to Cooper Kupp (2.36 yards of separation) and the 31-yard TD to Robert Woods (0.98 yards of separation).

Barr’s rough night was compounded by the continued errors in miscommunications between linebackers and cornerbacks that have allowed receivers to run wild. On the first Kupp touchdown, Mackensie Alexander never followed the Rams receiver on a crossing route, leaving Barr the last defender between Kupp and the end zone.

Alexander also missed a critical tackle the play before Trae Waynes didn’t get his head around on Kupp’s second touchdown of the night. Waynes also gave up a touchdown to Brandin Cooks, one play after Xavier Rhodes was pulled by Zimmer for unsportsmanlike conduct for kicking an official's flag after he was called for defensive holding.

It’s not just the back end where things have unraveled for Minnesota. The Vikings' star-studded defensive line has not been able to adequately pressure opposing quarterbacks since Week 1. Of course that job becomes more difficult without defensive end Everson Griffen, but the Pro Bowler is dealing with issues far more important than football right now.

If that unit is going to back the “next man up” mentality it preached all week, it needed to pressure Goff. Through three quarters, Minnesota sent in a blitz only six times. And in those three quarters, Goff was 20-of-25 passing for 398 yards and five touchdowns. The Cal product tied a record Thursday for the most touchdown passes thrown against the Vikings' defense in a game. Goff is the first QB to post a perfect passer rating against the Vikings while throwing more than seven passes.

The Vikings doled out $209.9 million in guaranteed money in 2018 and have five defensive players who hold top-10 salaries at their position (Barr, Rodes, Eric Kendricks, Danielle Hunter, Harrison Smith). Money isn’t everything, but if a team is paying top dollar, it expects top-notch play, which Minnesota has been without from its defense.

At this point of the season, the Vikings have lost their biggest strength; this defense has instead become a liability.