1st-and-10: Matt Nagy has a lot of work to do

As quarterback Mitch Trubisky struggled to sustain success with the Bears, most fans wrote him off as a misevaluated draft pick. But there was a faction of supporters who blamed coach Matt Nagy and his offense as the culprit, claiming poor offensive design and development dragged Trubisky down to the bust level.

The NFL weighed in on that matter in free agency, when no team even would give Trubisky a chance to compete for a starting job. Not one NFL team thought: ‘‘There’s a diamond in the rough that Matt Nagy screwed up. We’ll make a quarterback out of him.’’ Instead, Trubisky went straight from quarterback of the future to the retread bin.

But the Bears’ putrid offensive performance against the Bills in their second preseason game — especially reflected against Trubisky’s excellent performance — shed a different light on the situation. With Andy Dalton at quarterback, the Bears opened the game with four consecutive three-and-outs (37 net yards on 12 plays) before Dalton threw a 73-yard touchdown pass to Rodney Adams after they had fallen behind 28-0.

Sure, it’s only the preseason. The Bears’ offense was missing key starters, including receiver Allen Robinson, running back David Montgomery, right guard James Daniels and tight end Cole Kmet. But the Bills also were missing key starters, including quarterback Josh Allen and receivers Stefon Diggs, Emmanuel Sanders and Cole Beasley. And they still scored 34 first-half points against the Bears’ defense.

Why can’t the Bears do that? It’s not because of the quarterback; it’s because of the offense. With less than three weeks before the regular-season opener Sept. 12 against the Rams, the focus is not on Nagy picking the right quarterback but on Nagy producing an offense either one can succeed in. Justin Fields taking over a bad offense — whenever it happens — is likely to produce more hope than success.

At this point, there is more confidence that Fields can make a coach out of Nagy than Nagy can make a quarterback out of Fields. Last week, offensive coordinator Bill Lazor was asked what he wanted the offense to establish against the Bills.

‘‘I’d like to see us be able early in the game to run the ball for first downs,’’ Lazor said.

The Bears rushed five times for eight yards in the first half. It’s hard to tell which is the greater indictment, the eight yards or the five carries.

That’s not the only red flag. The protection issue that led to Fields getting crushed by Bills blitzing linebacker Andre Smith and could have been devastating was a familiar offensive failure. It happened against the Rams last season, when Nick Foles, facing a free blitzer, threw an incomplete pass to Darnell Mooney.

Foles could have hit the ‘‘hot’’ receiver, Robinson. Or, with a split-second more time, he could have led Mooney — who was about to burn cornerback Jalen Ramsey with a double move — for a 95-yard touchdown pass. Instead, it was an incompletion.

This time, it was a rookie quarterback. That time, it was a veteran quarterback being too aggressive in a moment of extreme decision. It’s the Bears’ offense under Nagy in a nutshell: There’s always something. Nagy has less than three weeks to get it together to give either quarterback a chance to succeed. At this point, it doesn’t matter which one.

2. Speaking of red flags: With less than three weeks before the opener, the Bears have three players competing for the starting job at left tackle. And each one is a major question mark.

Nine-time Pro Bowl player Jason Peters is a likely Hall of Famer, but he is 39, missed the last half of last season with a foot injury and was unsigned until the Bears called in desperation. Veteran Elijah Wilkinson has 26 NFL starts but none at left tackle; he has played right guard and right tackle in the NFL. Rookie Larry Borom had one start at left tackle at Missouri.

3. Peters is expected to be the Week 1 starter, but don’t discount Borom eventually taking over the job. The Bears had Borom rated much closer to second-round pick Teven Jenkins than most teams, for whatever that’s worth.

‘‘They’re both athletic. They’re both smart. They both work hard,’’ offensive line coach Juan Castillo said. ‘‘So there’s a chance that [Borom] could catch up just because he’s blessed with a God-given ability. . . . We’re not talking about just a solid player; we’re talking about being a good player to maybe even better, a Pro Bowl-type player.’’

4. You can’t blame the Bears for wanting to upgrade at left tackle, but they might miss veteran Charles Leno more than they thought. Since cutting Leno, who played 6,201 of 6,209 snaps in 95 consecutive starts since 2015, the Bears have had six players start at left tackle with the first-team offensive line: Arlington Hambright, Wilkinson, Borom, Alex Bars, Jenkins and Peters.

5. Trubisky was classy, as usual, after his triumphant return to Soldier Field. He passed on several opportunities to express even the slightest indignation about his tenure with the Bears, saying only that he was happier in Buffalo and comfortable with offensive coordinator Brian Daboll.

‘‘It’s been awesome,’’ Trubisky said. ‘‘Just learning from coach Daboll and executing his offense. I feel like every time he calls a play, it’s going to work. And you have to give credit to the other 10 guys on the field with me. Everyone’s doing their job.

‘‘I just feel comfortable and continue to grow and learn in this offense. It’s been a lot of fun working with coach Daboll. I’ve got a lot of trust and faith in him.’’

6. Though Dalton needs work with the first-team offense, it might be time for the Bears to switch from the Patrick Mahomes template to the Russell Wilson template in the preseason.

When Wilson was a rookie in 2012, Seahawks coach Pete Carroll — intrigued by Wilson’s performances as a backup — started him with his starters in the third preseason game. Wilson was stellar again — two touchdown passes and a 134.8 passer rating — and the rest is history.

Even if Dalton is the Week 1 starter, Fields has shown enough in the first two preseason games to warrant that same look. You never know.

7. The traditional ‘‘dress rehearsal’’ third preseason game is a thing of the past, so the Bears’ offense probably won’t face much of the Titans’ first-string defense, if at all, Saturday. But it still will be a test. The Titans have been coasting into the regular season — resting many starters, especially on offense — and have beaten the Falcons 23-3 and the defending Super Bowl champion Buccaneers 34-3.

Former Bears quarterback Matt Barkley, batting Logan Woodside for the backup job to Ryan Tannehill, has been red-hot (17-for-24, 169 yards, three touchdowns, no interceptions, 130.0 passer rating).

8. What, me worry? The Bears’ 41-15 loss to the Bills was their largest margin of defeat in the preseason since a 34-6 loss to the Seahawks in 2014. With offensive and defensive starters playing the entire first half of that game, the Bears trailed 31-0. The Bears went 5-11 in coach Marc Trestman’s second season and cleaned house.

9. Josh McCown Ex-Bears Player of the Week: Duh. Trubisky completed 20 of 28 passes for 221 yards with one touchdown and no interceptions for a 106.4 passer rating. He also scrambled for an 11-yard gain for a first down. His longest pass play was 26 yards to tight end Jacob Hollister. But the Bills scored six times on his seven first-half drives (four touchdowns and two field goals).

10. Bear-ometer: 7-10 — at Rams (L); vs. Bengals (W); at Browns (L); vs. Lions (W); at Raiders (L); vs. Packers (L); at Buccaneers (L); vs. 49ers (L); at Steelers (L); vs. Ravens (L); at Lions (L); vs. Cardinals (W); at Packers (L); vs. Vikings (W); at Seahawks (W); vs. Giants (W); at Vikings (W).