But even in the race's eleventh hour, strategists in both parties are struggling to figure out whether turnout will be closer to 2008 levels, when nearly 70% of eligible Wisconsin voters participated in the presidential election, or 2010, when voter turnout dropped to 49%.

CNN: Walker's fate in Wisconsin comes down to ground game

One is voter registration, which is at a record high, with 2.9m more eligible to vote this year than at the last election in 2002.

ECONOMIST: France's presidential race