U.S. Republican presidential hopefuls face off Tuesday in a televised debate, with former House of Representatives Speaker Newt Gingrich leading the pack in the latest polls.

The two-hour debate will focus on foreign policy and national security issues.

Going into the discussion, Gingrich has surged into first place in at least three national opinion polls , with former Massachusetts governor Mitt Romney not far behind. Georgia businessman Herman Cain is trailing in third after losing support amid sexual harassment allegations and public speaking blunders.

The three front-runners join five others in the debate Tuesday as they seek the Republican nomination and the chance to challenge President Barack Obama in next November's presidential election.

Romney is already making his case against President Obama with his first television ad of the campaign. The ad is airing in the state of New Hampshire — the scene of one of the first Republican presidential voting contests of the 2012 campaign and where Mr. Obama delivered a jobs speech Tuesday.

Romney's ad sharply criticizes Mr. Obama's record on the economy. But the White House hit back Tuesday, with press secretary Jay Carney accusing the Romney campaign of “blatant dishonesty” for taking something the president said out of context.

Romney's commercial shows Mr. Obama saying, “If we keep talking about the economy, we're going to lose.” But the full statement reveals Mr. Obama was actually quoting the campaign of his rival in the 2008 election, Senator John McCain.

The Quinnipiac University survey released Tuesday shows likely Republican voters believe Romney has the best chance to defeat Mr. Obama.