WASHINGTON (AP) — President Barack Obama returned to full-force camapaign today, ending a three-day pause to manage the federal response to the historic storm that battered the East Coast. He holds slim leads in many of the key U.S. battleground states five days before the November 6 election. Polling, however, also shows Obama locked in a tie nationwide with Republican challenger Mitt Romney, who tempered his criticism of the president this week to avoid the appearance of seeking political advantage in the midst of a natural disaster. Both candidates faced a day of trying to strike the right tone in an intensely stressful race. Obama's lead in a majority of the nine so-called battleground states could determine the outcome. Those states are neither reliably Republican nor Democratic, giving them outsized importance in the U.S. system for choosing the president . The winner is not the candidate with the most popular votes nationwide but the one who manages to accumulate at least 270 electoral votes in state-by-state contests. Those votes are determined by a combination of a state's population and representation in Congress. Despite a Romney surge nationwide after the three presidential debates, polling shows Obama holding on to leads in enough of the all-important swing states — most notably Ohio — to win at least the necessary 270 electors. No Republican candidate for the White House has ever won the election without capturing Ohio. Both candidates are battling to win over the thin slice of the electorate that remains undecided.