President Obama's approval rating remains ominously weak among the constituencies that could tip the battle for control of the Senate in November, the latest Allstate/National Journal Heartland Monitor Poll has found. In the latest poll, Obama also faces a formidable intensity gap that could foreshadow turnout challenges for Democrats: The share of adults who strongly disapprove of his performance (39 percent) is nearly double that of those who strongly approve (21 percent).