Hill: Environmental groups are warning President Obama that his liberal base might stay home on Election Day if he approves the Keystone XL oil pipeline. Proponents of the $5.4 billion Canada-to-Texas pipeline say their case is buoyed by the State Departments environmental analysis of the project, which was released to great fanfare last week. But critics say approval of the project could sow liberal discontent and hurt Democratic chances in 2014 including a host of contests that will likely decide...