Wesley Clark is closing in on his rival, the Democratic front-runner Howard Dean, according to a number of new polls that suggest support for the former general has soared in recent weeks.
Mr Dean still tops the Democratic field, but the 21-point lead he held over the former general and Nato chief less than a month ago has been narrowed to just four points, according to a Gallup poll conducted for USA Today and CNN.
General Clark is second in Democratic national polls, as well as in the vital New Hampshire primary, held on 27 January, where he trails Mr Dean by 17 points but is ahead of Senator John Kerry by six points.
Behind these numbers is a fluid situation that suggests General Clark has been making headway over other Democratic candidates, as Mr Dean's once seemingly unstoppable rise has been halted by a number of ill-considered comments and a concerted barrage of criticism from his opponents.
In a clear sign that the Dean campaign is starting to worry about General Clark's chances in New Hampshire, the first state to vote, staffers have been staking out his campaign appearances and passing out fliers and leaflets accusing him of being "pro-war" and questioning whether he was a "true" Democrat.
Jay Carson, Mr Dean's spokesman, said the campaign was simply "pointing out facts that the American people should know about".
In a comment presumably intended to rile the Dean camp, General Clark's pollster, Geoff Garin, later told reporters: "It would be a shocking development if Governor Dean did not win New Hampshire."
Earlier this week it was revealed that Mr Dean had shattered all Democratic fundraising records.
Although it represents a fraction of the money raised by President Bush, in the second half of 2003, the former Vermont governor raised $5m (£2.7m) a month, outstripping all previous Democratic contenders including Bill Clinton.
But while he is making money, Mr Dean has also been making trouble for himself with a series of badly received and apparently off-the-cuff comments.
He was also accused of being condescending to rural, white Southerners by implying they all drive pick-up trucks carrying a Confederate flag. He then claimed that the capture of Saddam Hussein had not made America safer.
His comments were seized on by his opponents as being inappropriate.
"The definition of a 'gaffe' in Washington is somebody who tells the truth but shouldn't have," he later said.
General Clark, meanwhile, has been furiously campaigning in New Hampshire and in the South, having decided not to campaign in Iowa, whose caucuses kick off the nation's primary season in 10 days' time.
His surge in New Hampshire has been most damaging to Mr Kerry, who was leading Mr Dean by a 2-1 margin in the state's polls just a year ago. His campaign has been widely criticised for failing to motivate voters, and Mr Kerry has been described as remote and aloof.
All the other main candidates have only polled single digits in New Hampshire, according to the most recent poll.
Joe Lieberman is at eight per cent, Dick Gephardt at six per cent, John Edwards at three per cent, Dennis Kucinich at two per cent, and Carol Moseley Braun and Al Sharpton at less than one per cent each.