Julian says : Events could produce sharp swings in the presidential race . He says Obama could be swayed by Europe crisis , high court decisions on health care . GOP leadership has potential to severely handicap the party 's eventual candidate , he says .
Julian Zelizer : Events could produce sharp swings in the presidential race . He says Obama could be affected by Europe crisis , high court ruling on health care . GOP feuding has potential to severely handicap the party 's eventual candidate , he says .