The single biggest reason Lovie Smith is no longer head coach of the Chicago Bears, apart from failures to reach postseasons, was a string of failures to bring a workable offense to Halas Hall. The single biggest task taken on by Phil Emery as general manager was upgrading that offense. It began in earnest about this time last year when Emery dealt away two third-round draft choices for wide receiver Brandon Marshall. A couple weeks later he spent heavily on a No. 2 running back in Michael Bush. A month later he traded up in the second round of the draft to select wide receiver Alshon Jeffery, then took tight end Evan Rodriguez in the fourth. That makeover of the Chicago offense escalated exponentially since the end of last season, accelerating financially and otherwise on Tuesday. From between two finalists from purely offensive backgrounds, Emery hired Marc Trestman to replace Smith. Among Trestman’s first hires was Aaron Kromer, offensive line coach with the annually high-powered New Orleans Saints offense.