I understand that there is a very good chance that many will call for Trestman's head, because the Bears have taken a significant step backwards this season. There is no way to deny this, but how much of that can be blamed on Trestman? Let's take a hard look at the Bears, and yes, any look at the Bears is hard to put myself through.
The offense has looked sloppy, but the skill position players are undoubtedly there to have a potent offense. Forte, Jeffery, Marshall, and Bennett are all good to great players, so you could complain about Bennett's blocking issues and no other receiver emerging as a potent option, but that is pretty nitpicky and nothing to dwell on.
The Bears offensive line is bad; actually, that's not fair; they're simply not good. It's not like anybody stands out as terrible, but the fact that nobody stands out as great (Kyle Long being the closest thing, but he's still working through inconsistency) limits the ceiling of what you can expect out of their performance. They benefited greatly from continuity last year, so even just a single doesn't make one spot worse, it contributes in making everyone worse. The Bears succeeded as a line, because they worked as a unit and knew how to pick up stunts and blitzes. When they got beat, it was getting beaten by talent as opposed to mental lapses. Now they are getting beaten in both ways, and it is really slowing down the offense, especially in the run game.
Then there's Jay Cutler. I have always been anti-Cutler, but let's recognize him for what he is: A perfectly average quarterback. He's Even Steven. He will flash some brilliance, and flash some idiocy. It all balances out, but in the end, he's somewhere around the 16th best quarterback in the league. But his strengths do not fit Trestman's system, which is all about timing and quick decisions. Jay holds onto the ball a little long, but also has a cannon of an arm. Trestman was apprehensive about committing to Cutler when he took the job, because he knew that he had these weaknesses. Still, it is really tough to go from a solid quarterback to a question mark at quarterback, and they decided their best option was to focus on the positive and bring back Cutler for what basically amounted to a three-year deal. It's easy to call this a bad decision now, but it's also hard to blame them for making it as there was no right answer.
And sadly, the offense is the positive side of things for the Bears. The defense is atrocious. The first year it was clear that the Bears didn't have enough talent. This year, they brought in more talent, but it has not been enough to make up for the regression. Let's go through the defense quickly, because it's really depressing to think about.
The defensive line is...fine. They have some intriguing guys in the middle with Ego Ferguson, Will Sutton, Stephen Paea, and Jeremiah Ratliff. The outside guys are solid with Willie Young flashing in games and Jared Allen being playable. They are not the issue.
The linebackers are the worst in football. They are not only the worst linebacking corps, they are probably the worst unit in football at any position. Lance Briggs doesn't have it, we can comfortably call Shea McClellin a bust, and I was unfortunately correct about Jonathan Bostic.
In the secondary, Kyle Fuller has flashed, but rookie cornerbacks always look like garbage, so there is no need to worry yet, but I also don't feel nearly as good about him as I do about the guy taken one pick earlier, Aaron Donald. Tim Jennings is okay for now, but a little known fact about Jennings is that he is a human, so every year, he gets older...by a year. The safeties put their pads on correctly every week. If the linebackers weren't so bad, this unit would be in the running for one of the worst units in football.
So this brings us back to Marc Trestman. Clearly, the Bears have taken a step back this year, but I still think that he should stick around. Continuity is key for most successful franchises, and giving Trestman two years isn't really fair to him or the franchise as a whole. Three years is a minimum that I personally set for any coach, and I would usually lean towards four. In all honesty, I don't see any realistic way that the Bears can be a Super Bowl contender next year. There are just too many holes on the roster. Because of that, there is no real benefit in bringing in a new coach without giving Trestman another chance.
The Chicago Bears may have a good coach in Marc Trestman, but it's going to take at least another year to find out.