Campaign officials estimated in February that Sen. Amy Klobuchar would need about $25 million to get through Iowa’s Feb. 3 caucuses and into New Hampshire’s Feb. 11 primary election. (Marci Schmitt — Associated Press/The Minnesota Star Tribune)

U.S. Sen. Amy Klobuchar, D-Minn., raised $5.2 million in the first seven weeks of her presidential candidacy, a total that passed an important test of campaign viability among political veterans as the 2020 Democratic field expands.

Fundraising success is an early measure of presidential candidates' prospects, and the number of individual donors is a mark of grassroots support. "It's a good effort and something that she should be proud of, and it makes her viable — very viable," said Mitchell Berger, a longtime Democratic fundraiser in Fort Lauderdale, Fla. "She has the resources and the ability to take it to the next step."

Klobuchar's average online contribution was $40, and 85 percent of donors gave less than $100, her campaign announced Monday.

Mike Erlandson, a former DFL Party chair, said Klobuchar met an important threshold for a candidate hoping to get traction in a crowded field. "These are very strong fundraising numbers, especially given she comes from a relatively small state," he said. Klobuchar's totals, he added, suggest "that she is going to remain solidly in the mix" as the race takes shape.

Vermont Sen. Bernie Sanders, who joined the race Feb. 19, topped the money race with $18.2 million, followed by California Sen. Kamala Harris' $12 million and former Texas Rep. Beto O'Rourke's $9.4 million.

Harris announced her candidacy Jan. 21, and O'Rourke declared on March 14 — meaning his donations came in over a shorter time span.

South Bend, Ind., Mayor Pete Buttigieg, who has captured immense media attention in recent weeks, rounded out the top four with $7 million. He said Jan. 23 that he was forming an exploratory committee. Klobuchar's announcement was Feb. 10. Her total narrowly exceeded that of New Jersey Sen. Cory Booker, whose candidacy began Feb. 1.

The deadline for filing contributions and expenditures during the first three months of the year is April 15. Many candidates release their numbers before the deadline, hoping to create momentum with donors and supporters.

Klobuchar connected with "almost 100,000 new supporters online," her campaign said in a statement. Her first-quarter report to the Federal Election Commission showed that Klobuchar transferred more than $3 million from her Senate re-election campaign last year, leaving her with $7 million in available cash.

A three-term senator, she had previously raised $10.6 million for her 2018 Senate campaign.

The numbers are "better than anybody could have expected or, frankly, could have hoped for," said Rick Kahn, a Klobuchar supporter who served as campaign treasurer for the late U.S. Sen. Paul Wellstone. Most telling, he said, were the online donations. "It's an organic thing" that reflects broad national interest in her campaign, he said.

Klobuchar said at an April 1 forum that she has defeated candidates with "a lot more money than me and a lot more connections than me. And I did it because I have grit."

Campaign officials estimated in February that she would need about $25 million to get through Iowa's first-in-the-nation caucuses next Feb. 3 and then into New Hampshire's Feb. 11 primary election.

Klobuchar has appeared at fundraising events in New York, California, Illinois, Nevada and elsewhere. Her campaign asks for contributions that can be spent during primary season and in the general election, maximizing the amount of money each supporter can give.

National polls and those in early-voting states have found single-digit support for Klobuchar. Low poll ratings can affect candidates' ability to raise adequate funds.

Wisconsin Gov. Scott Walker's 2016 Republican presidential campaign lasted just 71 days. He raised $8.5 million. In the 2012 campaign, Minnesota's Tim Pawlenty survived as a GOP candidate for 84 days. He raised $5.1 million.

But first-quarter numbers don't always foretell a campaign's future. Texas Sen. Ted Cruz led the Republican presidential fundraising race after the first quarter of 2015. Donald Trump didn't even enter the race until that June.

Klobuchar, who is not accepting donations from federal lobbyists or corporate political action committees, raised more than $1 million in the first 48 hours after launching her campaign. More than 95 percent was from people who gave less than $100.

Sanders outpaced the rest of the field in quick donations, accumulating $6 million the day after his campaign began. Former Vice President Joe Biden, who leads in most polls, has yet to formally enter the race.