U.S. Democratic presidential nominee Barack Obama is holding stable or growing leads over his Republican opponent John McCain in key states, but the national poll show the race may be tightening.
According to a CNN/Time survey released Thursday, Obama leads McCain among likely voters by 51 to 47 percent in Ohio, a 4-point margin that has not budged since last week.
He now leads McCain by 52 to 45 percent in Nevada and by 52 to 46 percent in North Carolina, margins which are both slightly larger than those reported in earlier polls.
The survey also show Obama leading McCain in Pennsylvania, the key blue state in which McCain is making a last-ditch, major push to score an upset, by a comfortable 12-point margin of 55 to 43 percent.
Meanwhile, there are signs the presidential race may be tightening.
CNN reported that according to an average of several recent surveys, Obama's lead over McCain is down to 5 points nationwide, 49-44 percent - a gap that is 3 points less than it was earlier this week, and nearly half what the margin was one week ago.
The closeness of poll results late in a presidential race is not unusual: John Kerry lost his 2004 White House bid despite holding a slim lead over George W. Bush in final days and in 2000 Al Gore trailed Bush by 5 points in early November before the two essentially split the vote days later.
"It's possible that McCain will continue to close the gap over the final few days of the campaign," said political researcher Alan Silverleib.
"Presidential elections often tighten up at the end, especially if there's not an incumbent on the ballot. Voters sometimes experience a degree of buyer's remorse' before settling on a new president," he said.
Historically, however, only one presidential candidate in modern history has come back from the deficit McCain faces to win an election -- Ronald Reagan in 1980.