By Fredreka Schouten, CNN

(CNN) -- EDITOR'S NOTE: This story was reported by the Center for Responsive Politics and CNN.

Donations from women to Democrat Joe Biden's presidential campaign surged as he picked California Sen. Kamala Harris as his running mate -- widening the gap in political giving between Biden and President Donald Trump, according to a new analysis by the nonpartisan Center for Responsive Politics for CNN.

The Biden-Harris ticket received more than $33.4 million in itemized contributions from women in August -- more than double the $13.7 million the Democrat's campaign had collected from female donors the previous month. (Contributions are "itemized" or disclosed, along with donors' identifying information, to federal regulators once donors contribute more than $200 to a candidate.)

By comparison, Trump's campaign raised far less money -- roughly $8.7 million in itemized contributions -- from women in August -- the month both he and Biden accepted their parties' nominations.

Biden announced Harris as his choice for vice president on August 11, and in interviews, some Democratic women donors described a concerted effort to flood the campaign with cash in support of Biden's choice. Among those making their presence known: Harris' sorority sisters, who have made more than 22,000 donations in increments of $19.08 -- marking the year, 1908, that Alpha Kappa Alpha Sorority, Inc. was founded at Howard University.

Women could be the decisive factor in a presidential election that's now a little more than a week away. Polls show Trump consistently lagging behind Biden in surveys of women voters. The President has pleaded openly for the support of what he calls the "suburban housewives of America." In recent weeks, he has even tried to lure them by arguing that he's helped protect the suburbs from low-income housing by overturning an Obama administration rule aimed at combating racial segregation.

The cash infusion in August helped Biden and his aligned party committees shatter the single-month fundraising record for a presidential contender and helped fuel an advertising blitz for the former vice president as the fall campaign swung into view.

New records

The lopsided support for the Biden-Harris ticket among female donors who give in larger amounts comes as women have stepped up their political activity more broadly. This year, a record 298 women are running in the general election for US House seats, topping the previous record of 234, set during the 2018 midterms, according to the Center for American Women and Politics at Rutgers University.

And women have contributed $2 billion to federal candidates in this cycle, surpassing the $1.3 billion they donated in 2016 when Democrat Hillary Clinton sought the presidency, according to the Center for Responsive Politics. So far, 44% of political donors in the 2020 cycle are women -- the highest share on record.

The tumultuous 2016 election helped drive women into politics, said Debbie Walsh, the director of the Center for American Women and Politics.

"They realized they need to have a role and a voice because this was a place affecting their lives and the lives of their families, and they couldn't sit on the sidelines," she said.

The month-by-month analysis of itemized contributions shows Biden starting to outraise Trump among larger women donors in March, as a string of primary victories solidified Biden's standing as the Democrats' standard-bearer and the pandemic upended normal activity.

The gap has only grown wider as Biden has outpaced the President in overall fundraising. And Biden and aligned Democratic committees entered the waning days of the campaign with a $107 million cash advantage over the President's fundraising operation, new filings show.

Neither campaign provided comment for this story.

The Center for Responsive Politics, a nonpartisan nonprofit that tracks money in politics, identifies donors' gender by applying an algorithm that compares the most popular US Census names to the names of donors reported to the Federal Election Commission. For the most part, donors' names and addresses are listed once they have contributed more than $200 to a presidential candidate's campaign committee. The analysis excludes any donors for whom gender could not be determined.

Trump traditionally has relied on small-dollar givers for a big share of his donations. But even when adding in contributions of $200 or smaller that show up in federal records filed by the online platforms aligned with each political party, ActBlue and WinRed, Biden still had an advantage over Trump in donations from female contributors through June of this year.

Giving groups The growing influence of women donors is no accident. Donors and strategists have worked for years help direct political money to female candidates.

For instance, Electing Women Bay Area -- a "giving group" with 100 members in Northern California -- financially supports Democratic women in competitive races. It's one of 17 such organizations around the country that form the Electing Women Alliance.

Other groups working to aid female candidates include Winning for Women, a group associated with former New Hampshire Republican senator Kelly Ayotte that works to elect conservative female candidates, and EMILY's List, a longstanding fundraising powerhouse that supports Democratic women running for office who back abortion rights.

"One of the things we have long stressed ... is this idea that men are used to writing the checks, and it's a muscle that has to be exercised," said Alexandra Acker-Lyons, who is Electing Women Bay Area's political director and runs her own philanthropic and political consulting firm. "Much like being a voter is a habit, being a donor is a habit."

The group helped several women who sought the presidency during the Democratic nomination battle and has hosted fundraisers for Senate candidates, including Iowa's Theresa Greenfield, Kansas' Barbara Bollier and Kentucky's Amy McGrath. All have outraised their Republican rivals.

Once it became clear that Biden intended to pick a female vice presidential nominee, some donors timed their contributions to make a big splash, said Stacy Mason, who serves as executive director of both Electing Women Bay Area and WomenCount, a crowd-funding platform for political giving.

"There were many, many people who held off in making their donations to the Biden ticket to show the world that we had her back and that we cared," said Mason, who herself waited to make a $2,800 donation to the Biden campaign until after the vice presidential choice was announced.

"The fact that it was Kamala made it even made it even more intentional," she said, "because we were, and obviously still are, in a moment in our country where we particularly wanted to show up for a black woman nominee."

Her group also scheduled a Zoom fundraiser for Harris on Sept. 1 that raised $1.25 million.

As a veteran California politician who served as San Francisco's district attorney and the state's first female attorney general before her election to the US Senate, Harris was no stranger to the group's donors. "It was a homecoming," Acker-Lyons said. "She knew more than half the people on the call."

A sisterhood of supporters

The Harris-Biden ticket also has drawn from another well of support: The sisters of the Alpha Kappa Alpha sorority that Harris pledged as a college student at Howard.

"Almost immediately, I started to see $19.08, $19.08, $19.08 on repeat," Clayton Cox, the Democratic National Committee's finance director, said of the stream of new donations that began popping up the day Harris joined the ticket.

More than 22,500 donations in increments of $19.08 have flowed into the Biden Victory Fund-- bringing in more than $430,000, DNC officials say. Biden Victory is a joint fundraising committee of the DNC and the Biden campaign.

"So many times in my fundraising life, we've had to push people to really do things," Cox said, "and this is completely self-organized and completely organic and a real testament to their sisterhood."

Michelle Arrington, an Atlanta attorney who pledged AKA at Howard a decade after Harris, has long supported Harris' political campaigns, dating back to her bid for California attorney general. Harris' push to promote research into uterine fibroids -- a condition Arrington has faced and that disproportionately afflicts Black women -- underscores the value of broad representation in government, she said.

Arrington helped host a fundraiser for Harris' presidential bid last year and wrote a check for $250 to the Biden campaign in August, shortly after the California senator joined the ticket.

But the informal movement to donate in amounts that reflects sorority's founding date was no surprise, she said. "It's indicative of the types of things we do: We'll start meetings at 12:08 or 7:08 p.m."

"It also demonstrated to the Biden campaign that, as sorority sisters of Sen. Harris, we were watching his campaign and that as Black women, our voices matter and we deserve to be heard," Arrington added. "We wanted the Biden campaign to know that is was us who will help carry Joe Biden and Sen. Harris to the White House.