When Hillary Clinton brought the Goo Goo Dolls to perform in front of a young donor crowd at Boston Symphony Hall last week, her campaign was taking direct aim at Barack Obama’s one remaining advantage — his fundraising prowess with small donors.

In a campaign where Mrs. Clinton’s team is hitting on all cylinders — New Hampshire polls, debate performance, speeches — only Mr. Obama’s ability to collect large numbers of small checks remains a threat to Mrs. Clinton.

Her most recent fundraising news was positive. Ben Smith of the Politico said of Mrs. Clinton, “the details are impressive, beating Obama in both categories: More overall dollars ($27 million to $22 million) and more primary dollars ($22 million) to ($19 million).”

Should Mrs. Clinton dominate each of the first four contests, Iowa, New Hampshire, South Carolina, and Nevada, the race will be over. If, however, Mr. Obama wins one of them or even far exceeds expectations (remember Bill Clinton, the self-proclaimed “Comeback Kid” didn’t win New Hampshire), small donors could be his life-line.

The Obama campaign attributes a considerable number of their 93,000 new donors to the Internet, the engine of small-dollar donation. The campaign says it has raised $74.9 million from 352,000 voters, which translates to roughly $212 a donation.

Senator Clinton has inherited her husband’s advantage with big donors. Under today’s federal giving limits, an individual can give a presidential candidate up to $2,300. But once they give that amount, they are done. Small donors, on the other hand, can be tapped again and again for funds as circumstances demand. The donor who started off with a $212 donation to Mr. Obama’s campaign could write nine more checks to his campaign. While most probably couldn’t afford to give that many checks, many could give at least once or twice more.

The heavy front-loading of this year’s primary season makes small donors even more important. Mrs. Clinton will battle to win in the first four primary contests. Her opponents will fight to stay alive. The survivors, probably only Mrs. Clinton and Mr. Obama, will then have to make tough decisions about where to spend money on February 5, when some 17 primaries will be held, including California, Florida, New York, and Michigan.

The scale of February 5 suggests that none of the other Democrats are in a position to challenge Mrs. Clinton. Even though John Edwards has made some attempts to attack her, his decision to accept federal matching funds served as an admission that his third quarter was not fruitful. This also may have scared off potential institutional endorsers, such as the 1.9 million members of the Service Employees International Union.

Unlike New Hampshire and Iowa, where campaign appearances and speeches by individual candidates make a difference, these February 5 contests will hinge on costly television advertising. California’s expensive television markets of San Diego, San Francisco, and Los Angeles offer daunting financial challenges to candidates. Early voting and the demands of a large “Get Out the Vote” operation present even more financing difficulties for candidates.

Events, such as Mrs. Clinton’s Symphony Hall fundraiser, suggest that her campaign is attempting to beat back even the small donor advantage of Mr. Obama. Mrs. Clinton’s partisans also are taking solace in that Mr. Obama didn’t perform better during the third fundraising quarter. While it’s difficult to measure, the slow-down in Mr. Obama’s fundraising seems to have begun after he stated at the YouTube debate that he would meet with foreign leaders, including the president of Iran, during his first year in office.

If there was a link between his slower fundraising pace and his poor debate performance, it could suggest that, contrary to the general perception, small, Internet-driven donors are less anti-establishment than thought. Or, more likely, it suggests that they, like major donors, are intensely focused on winning. Still, Mr. Obama’s support from small donors will enable him to exploit any potential flub, slip-up, or mistake from Mrs. Clinton in the event that she will make one.

Mr. Gitell (gitell.com) is a contributing editor of The New York Sun.