President Obama continues to lead Mitt Romney among likely voters, polls show, suggesting that the president has been able to maintain a post-convention bounce as the Republican candidate struggles to regain traction.

The polls come as Romney and Obama are set to face off in their first debate Wednesday in Denver. Voters give Obama an edge going into what is expected to be a key event, with 54 percent believing he will win the debate to 28 percent who think Romney will do better, according to a new poll by Quinnipiac University.

Such low expectations among voters could give Romney a boost among viewers who see the candidates side by side for the first time.

In the Quinnipiac poll, likely voters back Obama 49 to 45 percent over Romney, a lead that is partly based on Obama’s strong showing among women, a group that favors him by 18 points.

A CNN poll shows Obama reaching the 50 percent mark among likely voters and Romney getting the support of 47 percent. The poll results are within the margin of error.

The Romney campaign, as well as several conservatives, have dismissed a string of polls that show the Republican presidential candidate lagging, citing both bias and their own internal polling that Romney aides say shows a closer race.

According to the Quinnipiac poll, Romney maintains a slight lead among independent voters, 47 to 45 percent, and voters judge him better able to handle the budget deficit by 52 to 42 percent.

Romney has been highlighting the $16 trillion deficit at campaign events, often appearing with a ticking debt clock.

Yet the poll shows that Obama leads Romney on every other issue, among them health care, national security, the economy and handling an international crises.

Romney has been trying to chip away at Obama’s lead on foreign policy, for example by writing an editorial in the Wall Street Journal calling for a course change in the Middle East.

“In this period of uncertainty, we need to apply a coherent strategy of supporting our partners in the Middle East — that is, both governments and individuals who share our values,” Romney wrote in the editorial. “This means restoring our credibility with Iran. When we say an Iranian nuclear-weapons capability — and the regional instability that comes with it — is unacceptable, the ayatollahs must be made to believe us.”

Wednesday night’s 90-minute debate is slated to focus on domestic policy and the economy. But in recent days, Romney has signaled a broader focus.

“We cannot afford four more years like the last four years,” said Ed Gillespie, a senior adviser to the Romney campaign. “Whether it’s health care, energy, taxes and spending and debt, foreign policy, the message is we cannot afford four more years like the last four years.”

Even as national polls show a neck-and-neck race, polls in battleground states show a different story, with Obama opening up leads that are beyond the margin of victory.

Some 52 percent of likely voters across swing states side with Obama and 41 percent with Romney in the new Washington Post-ABC News national poll.

In New Hampshire, where Romney is seen by some as a favorite son because of his vacation home and ties to Massachusetts, Obama is outpacing his opponent by 15 points, a WMUR Granite State Poll shows.

John Sununu, an adviser to the Romney campaign, called the poll “a piece of garbage,” and “absolutely invalid” on MSNBC Tuesday morning, predicting a two- to three-point Romney victory in New Hampshire, a state Obama won in 2008 over Sen. John McCain.