Associated Press
Republican presidential candidate, former Massachusetts Gov. Mitt Romney speaks at a campaign rally in Bellevue, Wash., Friday, March 2, 2012.

WASHINGTON (MCT) — After locking up much of the Republican establishment's heavyweight fundraisers, Mitt Romney is going after the little guy.

"Donate $3 today to be automatically entered to be Mitt's special guest for Election Night on Super Tuesday," reads an email appeal from the Romney campaign to supporters. A dramatic new Web video asks for $20 contributions to fight the "Obama Attack Machine."

The GOP presidential candidate made a similar solicitation after clinching the Michigan primary Tuesday, with a rare personal plea for people to visit his website and "pledge your support — in every way possible."

The pitch reflects a challenge for Romney, one of the wealthiest candidates ever to run for president: He so far has been unable to build a broad base of small donors who can inject fresh cash into his campaign. The challenge has grown more acute as he heads into next week's Super Tuesday, with contests in 10 states, and subsequent battles in the fight for the GOP nomination.

Although he has outstripped his Republican rivals in fundraising, he also is burning through cash. Romney spent money nearly three times faster than he raised it in January, leaving him with $7.7 million. Since then, his campaign has shelled out at least $2.7 million for television advertising alone, according to sources familiar with the ad buys.

Romney, who put more than $40 million of his own money into his 2008 White House bid, has not yet pulled out his checkbook this year. Campaign officials declined to say whether he was considering doing so.

So far, the former Massachusetts governor has relied on a network of wealthy contributors to finance his run. Just 9 percent of the nearly $63 million Romney raised through the end of January came from supporters who gave $200 or less, according to an analysis by the nonpartisan Campaign Finance Institute.

In contrast, almost half the money given to his GOP rivals Rick Santorum and Newt Gingrich, as well as President Barack Obama, came from small donors.

Romney's campaign is trying to reverse that imbalance by soliciting single-digit donations via the Web. That's a tactic regularly used by the Obama campaign to gather new email addresses for future fundraising.

But capturing the enthusiasm of small donors requires a candidate to ignite the base, and some Republican fundraisers say that's something Romney has so far failed to do.

"Money comes in when something revolutionary has happened, when lightning strikes," said Peter Pasi, a GOP digital fundraising consultant whose clients this year include Santorum. "You have to have a bottle to catch the lightning — but there needs to be lightning there in the first place."

Romney's wealth, which he has pegged at "between $150 (million) and $200 some odd million," could work against him.

"When he says, 'I need three bucks,' does it seem real?" Pasi asked.