President Barack Obama returned to full-force campaigning Thursday, 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 Nov. 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 while ensuring that their supporters go to the polls. Superstorm Sandy was bound to hurt turnout in hard-hit New Jersey and New York, but both are heavily Democratic, and it was unlikely to have a significant effect on results. Election officials were promising every effort to have polls open or direct voters to alternative locations where necessary.

This week's storm, and the federal government response to the devastation, could serve to cause voters to make up their minds.

The contest between Obama and Romney, at heart, has been an argument over the role of the federal government in the lives of Americans. Obama believes Washington can have a positive effect. Romney believes the government should become much smaller and, therefore, collect much less in taxes.

Obama has been given high marks, even from some of his harshest Republican critics, for his handling of this week's storm crisis and the dispatch of massive federal aid to victims. Romney has been forced to answer questions about his earlier campaign statements that the key federal emergency relief organization, the Federal Emergency Management Agency or FEMA, should turn its role over to the states.

As his campaign resumes, Obama will try to make up for lost time with a heavy travel itinerary in the coming days, including rallies Thursday in Wisconsin, Nevada and Colorado.

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President Barack Obama stops to greet a small child in a dragon costume during a campaign event at Austin Straubel International Airport in Green Bay, Wis., on Thursday. (Pablo Martinez Monsivais/Associated Press)

Obama spokeswoman Jennifer Psaki said the president remains focused on the storm recovery, but must resume campaigning because of the "reality" of Tuesday's election and the need to continue making the case for Americans to give him four more years in the White House.

The partisan sniping continued this week from the candidates' surrogates and their running mates. Much of it focused on Romney's new television and radio ads in critical Ohio that suggest automakers General Motors and Chrysler are adding jobs in China at the expense of workers in the Midwestern swing state. Vice-President Joe Biden said the spots were "one of the most flagrantly dishonest ads I can ever remember."

Even automakers protested the ads.

Obama's campaign planned to keep pressing its criticism of the ads as it seeks to block Romney's prospects for a breakthrough in Ohio and other Midwestern states where the auto industry is deeply important to the economy, the most important issue in the 2012 election.

The Republican ticket hasn't backed away from the ad. Running mate Paul Ryan said in a statement that "American taxpayers are on track to lose $25 billion as a result of President Obama's handling of the auto bailout, and GM and Chrysler are expanding their production overseas."

In fact, Chrysler is adding 1,100 jobs to its plant in Toledo, Ohio. It's also adding production facilities in China as demand for cars there grows. Because of trade rules, it's easier for companies to build cars for the Chinese market in China. It's also more efficient. Japanese automakers, for example, have plants in the U.S. to meet American demand.

Romney was campaigning Thursday in Virginia, while Ryan was appearing at events in Nevada and Colorado.

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Republican presidential candidate, former Massachusetts Gov. Mitt Romney greets supporters, including one wearing an elephant hat, left, as he campaigns at Integrity Windows in Roanoke, Va., on Thursday. (Charles Dharapak/Associated Press)

Biden had two events scheduled in Iowa. Obama was starting his day in Wisconsin, making up an event that was cancelled earlier in the week because of the storm. He had a rally planned later in Las Vegas, as well as Boulder, Colorado, a heavily Democratic area.

More than 19 million people have already voted in the presidential, either by mail or in person. No votes will be counted until Nov. 6, but some key states are releasing the party affiliation of those who have voted.

Democrats have an edge in votes cast in battleground states Florida, Iowa, Nevada, North Carolina and Ohio. Republicans have an advantage in Colorado.