Today's contest
Pennsylvania Democratic primary
Voting: 7 a.m.-8 p.m. EDT
At stake: 158 pledged delegates
The race: Hillary Clinton leads in most polls by single digits, but probably needs a bigger win to reenergize her campaign. She is counting on support from blue-collar white voters in central and western Pennsylvania. Barack Obama has cut into Clinton's lead and, if he pulled off an upset, could force her from the race. He is expected to do well in Philadelphia, particularly among African-Americans. The battleground could be the suburban counties ringing Philadelphia. 