BURLINGTON, Massachusetts (AP) ― President Barack Obama and Republican Mitt Romney are embarking on a week heavy with travel through battleground states and appeals to key constituencies, with both campaigns wrangling over unrest in the Middle East and who is best equipped to rejuvenate the economy.

Both candidates are courting voters in a series of must-win states and reaching out to a number of voting groups that could determine the election, from working-class white voters in states like Ohio and Wisconsin to Latino voters in Florida and viewers of a popular Spanish-language television network.

The winner of the U.S. presidential election is not determined by national popular vote, but by a series of state-by-state contests, making victory in battleground states such as Ohio and Florida particularly important.

Obama and Romney have dueled for an advantage on foreign policy, with attention focused on unrest in the Middle East in reaction to an anti-Muslim video that led to the storming of several U.S. diplomatic posts, including the embassy in Cairo, Egypt, and the killing of four Americans, including the U.S. ambassador to Libya, in the eastern Libyan port of Benghazi.

Romney’s campaign has pointed to the events in Egypt and Libya as evidence of national security weakness from the Obama administration. Susan Rice, the U.S. ambassador to the United Nations, defended the administration on Sunday television talk shows, calling the critique a “very empty and baseless charge of weakness.”

Romney and Obama have also tangled over China, each accusing the other of supporting policies that would move American jobs overseas. Romney released a television advertisement last week assailing Obama for “failing American workers” and ignoring unfair trade practices by China. Obama responded with an ad accusing Romney of outsourcing jobs to China when he worked in the private sector.

Obama was kicking off a week of travel in Ohio on Monday, with stops planned in Cincinnati and Columbus.

The president was raising campaign cash in New York on Tuesday, followed by events in Florida on Thursday, Virginia on Friday and Wisconsin on Saturday ― all states that Obama carried in the 2008 election.

Obama was making his first trip to Wisconsin in months and his most pronounced pitch to voters there since Romney chose Wisconsin Rep. Paul Ryan as his vice presidential running mate. Wisconsin has not voted for a Republican presidential candidate since President Ronald Reagan in 1984 and is considered one of Romney’s most enticing electoral targets.

Romney’s itinerary included fundraising stops in the Los Angeles area on Monday along with outreach to key Latino voters, including an address to the United States Hispanic Chamber of Commerce and an interview with Spanish-language television network Telemundo. The network interviewed Obama last week.

Romney was also expected to hold fundraising events in Utah and Texas before heading to Florida for fundraisers later in the week.

Both campaigns have competed vigorously for voters in eight toss-up states likely to decide the election: Ohio, Florida, Virginia, Iowa, New Hampshire, Colorado, Nevada and North Carolina. The states have dominated the candidates’ attention in travel and advertising.

Romney spent several hours at a Boston-area hotel with advisers on Sunday, prompting speculation that he was preparing for the upcoming presidential debates. The first debate, considered a crucial showdown between Romney and Obama, will be held Oct. 3 in Denver.

Ohio Sen. Rob Portman, who is playing the role of Obama in Romney’s debate preparation, joined Romney on a Friday night flight to the Boston area. Romney officials would only say the former Massachusetts governor was holding “private meetings.”

Romney had planned to hold a rally in Pueblo, Colorado, later Sunday, but the event was cancelled after a small aircraft crashed at the Pueblo airport. The event was scheduled to be held at an aircraft museum near the airport. Romney spokesman Rick Gorka said the campaign did not want to interfere with the investigation or any emergency response efforts.