Senior Democratic officials are expressing serious concerns about the political risks posed by Barack Obama’s acceptance speech at Invesco Field at Mile High Stadium Thursday evening. From the elaborate stagecraft to the teeming crowd of 80,000 cheering partisans, the vagaries of the weather to the unpredictable audience reaction, the optics surrounding the stadium event have heightened worries that the Obama campaign is engaging in a high-risk endeavor in an uncontrollable environment. A common concern: that the stadium appearance plays against Obama’s convention goal of lowering his star wattage and connecting with average Americans and that it gives Republicans a chance...