A tumultuous election season that tugged again at America’s searing political divides and raised questions about its commitment to a democratic future comes to a close on Tuesday as voters cast ballots in the first national election of Joe Biden’s presidency. With polls open, Democrats were braced for disappointing results, anxious that their grip on the U.S. House may be slipping and that their hold on the U.S. Senate — once seen as more secure — has loosened. The party’s incumbent governors in places like Wisconsin, Michigan and Nevada are also staring down serious Republican challengers. Re…