US Republican presidential candidate Mitt Romney's recent bounce in the polls after his dominant performance at last week's first presidential debate may prove to be short lived, experts said.

President Barack Obama on Tuesday led the challenger by only a razor-thin 0.5 point margin, further narrowing the gap from the previous day's 1 point and the previous week's 3 points, according to Real Clear Politics' poll average.

Many pundits, politicos and experts believe Romney's gains stem from his strong showing in last Wednesday's nationally televised debates against Obama, as well as the president's weak performance in which critics said he seemed disinterested.

But the question remains whether the contender's post-debate bounce will last, as the Nov. 6 election day is still four weeks away.

"Debate bounces generally don't last very long because they are superseded by actual events and later debates," said Darrell M. West, director of governance studies at the Brookings Institution. "Romney did well in presenting himself, but he has opened himself up to flip-flop charges because he has changed his positions on tax cuts, health care, and education."

If Obama does well in the next two debates, it will reverse Romney's gains, West said.

Steven Kull, director of the Program on International Policy Attitudes at the University of Maryland, said such bounces tend to last a week or two.

"Then it's a question of what comes in its place," he said.

For example, if Romney builds on last week's momentum, the bounce could last longer, but if he fails to do so, or if team Obama derails Romney somehow, the challenger could lose his boost in the polls, Kull said.

Various members of team Obama made television appearances shortly after Wednesday's debate, charging Romney with lying during the debate on issues such as tax cuts. It is unclear yet whether the strategy is having an impact, however.

Moreover, polls show that Americans do not like negative campaigning, although Kull pointed out that individuals still may be influenced by it.

John Fortier, director of the democracy project at the Bipartisan Policy Center, said calling Romney a liar is unlikely to work well for Obama. There are some reasonable disagreements and characterizations of both campaigns about each other's plans, he said. And Americans will have a hard time sorting out this disagreement over accuracy.

"Better for the president to show that his plans will help the economy while Romney's will not," Fortier said.

Kull noted it is also important to pay attention to what is happening in the swing states, and Obama is so far ahead in those states that he is unlikely to lose them.

Fortier noted that several incumbent presidents have lost the first debate and then gone on to win, so Romney's strong performance is helpful to him but will not determine the election.

Reagan and George W. Bush both stumbled early in debates, but came back to win.

Romney's unexpectedly strong performance in last week's debate breathed new life into his campaign, just as donors were starting to show signs of shifting funds toward GOP Senate race candidates.

But despite his recent surge ahead, Romney must continue to build on his victory, Republican strategist Ford O'Connell said.

This debate was a good start but Romney's got a long way to go, he said, adding that Romney must continue selling himself as a principled but practical candidate willing to work across party lines.