For one piece of evidence of an enthusiasm gap between Mitt Romney and his rivals for the GOP presidential nomination, look no further than his campaign’s financial report.

At first glance, the numbers may seem like good news for Romney, given that he is by far the strongest fundraiser in the field. Through the end of January, he had raised $63.2 million for his campaign, more than twice as much as the next most successful Republican candidate, Rep. Ron Paul (Tex.), who had raised $30 million. Newt Gingrich had brought in $18.2 million, and the figure for Rick Santorum was $6.7 million.

But look more deeply at the numbers, and a trend emerges: Romney is getting considerably less support from small-dollar donors, those who give less than $200 at a time.

These small donors, unlike those who write giant checks, don’t give because they’ve been invited to a fundraiser to meet the candidate. They typically donate out of excitement for the campaign — and they’re the type of supporters who will help by volunteering their time and talking to friends and neighbors about the race.

“This is not just about money,” said Michael Malbin, who studies small donors at the nonpartisan Campaign Finance Institute. “It’s a symptom or a symbol of something that’s more important generally in politics. There’s a large overlap between the kind of people who give $50 and $100 and the kind of people who volunteer.”

Paul, Gingrich and Santorum all have raised more than half of their money from small donors. Romney’s campaign, by contrast, has brought in just 12 percent of its total from contributors giving less than $200 at a time.

Romney is raising even less from small donors than he did during his 2008 effort. In that campaign, 25 percent of his fundraising came from those supporters, according to a Washington Post analysis of federal filings.

A Romney aide dismissed the idea that the former Massachusetts governor lacks small-dollar contributors, citing internal figures showing that 105,723 people have given $250 or less to the campaign.

Besides being a sign of enthusiasm among average Americans, small donors are an important source of money for campaigns. That’s even more true now, during the heat of the primary season, when the candidates have less time to travel to host events that bring in bigger checks.

Small donors often are most willing to open their pocketbooks after big wins for their candidates. That explains how Romney’s competitors were able to narrow their gap in fundraising with him last month, according to figures reported to the Federal Election Commission this week. In the fourth quarter of last year, Romney raised as much as his three current rivals combined. Last month, he barely beat each of them individually.

And Romney has relied heavily on donors giving the maximum $2,500 allowed by law, meaning he can’t hit them up again for more cash.

Santorum told reporters on Tuesday that his campaign has raised “well over $6 million” so far in February. That means he may already have beaten the $6.4 million that Romney brought in last month.

However, Romney also has stepped up fundraising after the rush of primaries and caucuses in January. Last week, he joined top fundraisers and Donald Trump at a Manhattan law firm to call potential donors.

If Romney wins the Republican nomination, his weak small-donor fundraising will contrast with that of President Obama, who has made small donors the base of his campaign fundraising. Obama’s campaign raised 70 percent of its money from small donors through January — an even higher rate than in his 2008 bid.

However, the emergence of super PACs, which aren’t subject to the $2,500 limit on donations to campaigns, may give Romney an overall advantage in the end. Romney has so far gotten the most help from the PACs, which must operate independently from campaigns under federal law.

Obama only recently endorsed the efforts of a super PAC operating on his behalf. The group has posted anemic fundraising compared with Republican efforts. Figures show that the PACs supporting Republicans in the presidential race have raised $89.2 million in this election cycle, compared with $4.2 million for the pro-Obama group.