But as Democrat Martha Coakley and Republican Scott Brown head into the rare mid-January race, just who will show up at the polls remains something of a mystery.
“Conventional wisdom is, the high turnout favors the Democrat. But in a special election, high turnout is volatile because you don’t know who’s showing up,” said Scott Ferson, a Democratic strategist in the state.
Making the vote even tougher to predict: the weather. Tuesday’s forecast calls for a mix of snow and rain, with temperatures in the low 30s.