(CNN) Sen. Elizabeth Warren's second quarter fundraising was massive: The presidential candidate raised $19.1 million in a three-month period, a stark contrast from the first quarter of the year when she raised just over $6 million.

The details in the report Warren's campaign filed with the Federal Election Commission late Monday offer something of a roadmap of where Warren's cash came from, how she spent the money and what might have helped drive the senator's fundraising success.

Her total haul is particularly noteworthy given that the Massachusetts Democrat has declined to hold any high-dollar fundraisers or solicit wealthy donors this year. She outraised -- by about $1 million -- Vermont Sen. Bernie Sanders, the other candidate in the 2020 field who is currently pursuing a grassroots-only fundraising strategy.

The most recent quarter showed that Warren's bet on a small-dollar fundraising strategy is working for now, allowing her to compete with some of her rivals, like former Vice President Joe Biden and South Bend, Indiana, Mayor Pete Buttigieg, who have aggressively courted wealthy donors.

The clues below only offer a snapshot of Warren's fundraising because the FEC only requires campaigns to itemize contributions larger than $200. The Warren campaign itemized about $6.4 million of the more than $19 million raised in the second quarter because the great bulk of the donations she pulled in -- more than $12 million -- came in amounts of $200 or less.

Still, the spikes in itemized donations may tell us when and why her smaller-dollar donations surged.

When Warren called for impeachment proceedings against Trump in April, there was a fundraising spike

Warren made waves in April when she came out as the first major Democratic presidential candidate to call for impeachment proceedings against President Donald Trump, after the release of a redacted version of special counsel Robert Mueller's Russia report. While the announcement drew praise from pro-impeachment voters, the move was also seen as politically risky. Warren's FEC report shows that it resulted in a spike in fundraising.

Consider that in the week leading up to that Friday in April, Warren raised an average of around $24,000 per day (again, this is only taking into account the itemized donations that are greater than $200 -- a fraction of Warren's total fundraising and therefore an incomplete picture).

On the Friday that Warren called for impeachment proceedings, she raised almost $94,000 in a single day from donations greater than $200. The next day, she pulled in more than $105,000.

Other money-raking days: Student loan debt cancellation plan, first Democratic debate

The following are some other strong fundraising days for Warren, and our best guess as to what could have contributed to the cash influx on those days (another reminder that the following daily hauls only represent donations that were more than $200):

April 22: $114,000 -- Warren releases major student loan debt cancellation plan and participates in CNN town hall

$114,000 -- Warren releases major student loan debt cancellation plan and participates in CNN town hall May 28 and 29: $116,000 and $109,000 -- Reproductive rights was already making national headlines, and Warren had already released a plan to protect access to abortion earlier in the month. On May 28, she tweeted about the potential closure of Missouri's last abortion clinic

$116,000 and $109,000 -- Reproductive rights was already making national headlines, and Warren had already released a plan to protect access to abortion earlier in the month. On May 28, she tweeted about the potential closure of Missouri's last abortion clinic May 31: $106,000 -- The day before, Warren appeared on "The View," where she unveiled a universal childcare calculator

$106,000 -- The day before, Warren appeared on "The View," where she unveiled a universal childcare calculator June 26: $157,000 -- Warren made a last-minute decision to visit the Homestead migrant detention facility in South Florida, hours before she took the stage at the first Democratic debate.

$157,000 -- Warren made a last-minute decision to visit the Homestead migrant detention facility in South Florida, hours before she took the stage at the first Democratic debate. June 27: $166,000 -- Day after her debate appearance

Overall, Warren had her strongest fundraising stretch of the quarter in the final week ahead of the second quarter deadline.

Warren spent millions on staff, online ads

Warren spent $2.6 million on staff salaries alone in the second quarter -- a sizable chunk of the $10.6 million she spent over those three months. That's almost as much as what Julian Castro raised in the entire quarter and doesn't even account for the additional $1.2 million in payroll taxes.

Her campaign previously told CNN that they now have more than 300 campaign staff, with some 60% of them in the four early states of Iowa, New Hampshire, South Carolina and Nevada.

Warren has one of the biggest payrolls among all the candidates in the giant Democratic field -- both a sign of her early robust organizing, but also a reminder of how costly paying those staffers will continue to be.

In the first six months of the year, Warren's campaign also spent more than $2.9 million on Facebook and Google ads.

Photos: Former presidential candidate Elizabeth Warren Photos: Former presidential candidate Elizabeth Warren Elizabeth Warren, a US senator from Massachusetts, speaks during a campaign event in March 2019. Hide Caption 1 of 45 Photos: Former presidential candidate Elizabeth Warren Warren is held by her father, Donald Herring, soon after she was born in Oklahoma City in 1949. "My daddy worked hard his whole life," Warren said when she posted this picture to Facebook on Father's Day 2014. "He sold fencing and carpeting, and ended up as a maintenance man. He and my mother never had much, but he said that his life was a success because his four kids had more opportunities than he had." Hide Caption 2 of 45 Photos: Former presidential candidate Elizabeth Warren A young Warren sits with her mother, Pauline. "When I was 12, my daddy had a heart attack," Warren wrote on Facebook in 2017. "All three of my brothers were off in the military, and Daddy was out of work for a long time. We lost our family station wagon, and we were about an inch away from losing our home. One day, I walked into my mother's room and found her crying. She said, 'We are not going to lose this house.' She wiped her eyes, blew her nose, and pulled on her best dress -- the one she wore to funerals and graduations. At 50 years old, she walked down the street and got her first paying job: answering the phones at Sears. That minimum wage job saved our home, and my mother saved our family." Hide Caption 3 of 45 Photos: Former presidential candidate Elizabeth Warren Warren poses for a Christmas photo with her brother John. All three of her brothers served in the military. Hide Caption 4 of 45 Photos: Former presidential candidate Elizabeth Warren In the late 1960s, Warren attended George Washington University on a debate scholarship. She dropped out after two years to get married, but she graduated from the University of Houston in 1970. Hide Caption 5 of 45 Photos: Former presidential candidate Elizabeth Warren Warren holds her newborn daughter, Amelia, in 1971. She and her first husband, Jim Warren, had two children before divorcing in 1980. Hide Caption 6 of 45 Photos: Former presidential candidate Elizabeth Warren Warren with her three brothers -- Don, John and David -- in 1980. After graduating from college, Warren worked as a speech pathologist at a New Jersey elementary school. She then got a law degree and taught at the Rutgers School of Law before becoming a professor at the University of Houston Law Center. She's also been a professor at the University of Texas Law School, the University of Pennsylvania Law School and Harvard Law School. Hide Caption 7 of 45 Photos: Former presidential candidate Elizabeth Warren Warren and her second husband, Bruce Mann. She posted this old photo to Facebook in 2016 along with a story about how she proposed to him. They were married in 1980. Hide Caption 8 of 45 Photos: Former presidential candidate Elizabeth Warren Warren teaches at the University of Pennsylvania Law School in the early 1990s. Hide Caption 9 of 45 Photos: Former presidential candidate Elizabeth Warren US Sen. Barack Obama listens to Warren speak during a roundtable discussion about predatory lending in 2008. Warren is an expert on bankruptcy law and was an adviser to the National Bankruptcy Review Commission in the 1990s. In 1989, Warren co-authored the book "As We Forgive Our Debtors: Bankruptcy and Consumer Credit in America." Hide Caption 10 of 45 Photos: Former presidential candidate Elizabeth Warren Warren takes her seat to testify before the House Budget Committee in 2009. The United States was battling a recession at the time, and Warren had been appointed to a congressional oversight panel overseeing the $700 billion Troubled Assets Relief Program. Hide Caption 11 of 45 Photos: Former presidential candidate Elizabeth Warren Warren and Treasury Secretary Timothy Geithner listen to President Barack Obama at the White House in September 2010. Obama was appointing Warren to be his assistant and special adviser to the Treasury Secretary in order to launch the Consumer Financial Protection Bureau. Warren had long called for a federal agency designed to protect consumers from fraudulent or misleading financial products. Hide Caption 12 of 45 Photos: Former presidential candidate Elizabeth Warren Warren and US Sen. Scott Brown, right, make fun of each other during an annual St. Patrick's Day breakfast in Boston. Warren announced in 2011 that she would be challenging Brown for his Senate seat.. Hide Caption 13 of 45 Photos: Former presidential candidate Elizabeth Warren Warren speaks to constituents at a campaign event in Scituate, Massachusetts, in May 2012. Hide Caption 14 of 45 Photos: Former presidential candidate Elizabeth Warren Warren takes a morning walk with her dog Otis on the Harvard University Business School campus in May 2012. Hide Caption 15 of 45 Photos: Former presidential candidate Elizabeth Warren Warren stands with family members after giving a speech in Springfield, Massachusetts, in June 2012. Warren has several grandchildren. Hide Caption 16 of 45 Photos: Former presidential candidate Elizabeth Warren President Barack Obama greets Warren at a fundraiser in Boston in June 2012. Hide Caption 17 of 45 Photos: Former presidential candidate Elizabeth Warren Warren speaks at the Democratic National Convention in September 2012. Hide Caption 18 of 45 Photos: Former presidential candidate Elizabeth Warren Warren greets supporters during a campaign event at Boston University. Hide Caption 19 of 45 Photos: Former presidential candidate Elizabeth Warren Warren takes the stage after defeating Brown for a Senate seat in November 2012. Hide Caption 20 of 45 Photos: Former presidential candidate Elizabeth Warren Warren listens during a hearing of the Senate Committee on Banking, Housing and Urban Affairs in May 2013. Hide Caption 21 of 45 Photos: Former presidential candidate Elizabeth Warren Warren meets with Supreme Court nominee Merrick Garland in April 2016. Hide Caption 22 of 45 Photos: Former presidential candidate Elizabeth Warren Warren campaigns with Democratic presidential candidate Hillary Clinton in June 2016. Hide Caption 23 of 45 Photos: Former presidential candidate Elizabeth Warren Warren, a member of the Senate Banking Committee, questions Wells Fargo CEO John Stumpf in September 2016. Warren unleashed a verbal barrage at Stumpf, calling the embattled bank boss "gutless" and demanding he step down. Her diatribe was the most forceful condemnation yet of Wells Fargo, who fired more than 5,000 employees over the years for creating fake accounts without customer knowledge. The employees created the fraudulent accounts to meet bank quotas and were allegedly threatened with firing if they didn't comply. Hide Caption 24 of 45 Photos: Former presidential candidate Elizabeth Warren In January 2017, Warren posted this photo of her and Obama together. Obama was leaving after two terms as President. Hide Caption 25 of 45 Photos: Former presidential candidate Elizabeth Warren Warren holds a transcript of her speech in the Senate Chamber after she was cut off during the debate over Attorney General-designate Jeff Sessions in February 2017. In an extremely rare rebuke, Senate Majority Leader Mitch McConnell silenced Warren after he determined that she violated a Senate rule against impugning another senator. Warren was reading from a 1986 letter in which Coretta Scott King, the widow of Martin Luther King Jr., was critical of Sessions -- who at the time was a nominee to be a federal judge. Hide Caption 26 of 45 Photos: Former presidential candidate Elizabeth Warren Warren and other Democrats listen as President Donald Trump speaks to a joint session of Congress in February 2017. Hide Caption 27 of 45 Photos: Former presidential candidate Elizabeth Warren US Sen. Bob Corker talks with Warren during a Senate committee hearing in June 2017. Hide Caption 28 of 45 Photos: Former presidential candidate Elizabeth Warren Warren attends a confirmation hearing for Jerome Powell, who was nominated to be chairman of the Federal Reserve, in November 2017. It was a day after President Donald Trump referenced Warren as "Pocahontas" during an event honoring Navajo code talkers. Conservatives have long criticized Warren for claiming that she is part Native American, and the senator's heritage became an issue during her Senate campaigns. Trump seized on the attacks and has regularly mocked Warren by calling her "Pocahontas." In October 2018, Warren released results of a DNA test showing she has distant Native American ancestry. The DNA results claimed "strong evidence" of Native American ancestry "6-10 generations ago." But it only served to intensify the criticism given her distant ties. Hide Caption 29 of 45 Photos: Former presidential candidate Elizabeth Warren Warren runs down Boston's Clarendon Street waving to crowds during the annual Boston Pride Parade in June 2018. Hide Caption 30 of 45 Photos: Former presidential candidate Elizabeth Warren Warren and US Sen. Susan Collins ride the Senate subway in June 2018. Hide Caption 31 of 45 Photos: Former presidential candidate Elizabeth Warren Warren is seen in the sunglasses of Arian Rustemi during a rally in Boston in June 2018. Warren was calling for the swift reunification of children and parents who had been separated at the US-Mexico border. Hide Caption 32 of 45 Photos: Former presidential candidate Elizabeth Warren Warren helps Georgia gubernatorial candidate Stacey Abrams make calls to voters in October 2018. Hide Caption 33 of 45 Photos: Former presidential candidate Elizabeth Warren A Warren figurine sits in the back pocket of Mary Jo Kane during a town-hall event in Boston in October 2018. Hide Caption 34 of 45 Photos: Former presidential candidate Elizabeth Warren Warren was re-elected in 2018. Here, she is joined by her husband, Bruce Mann, as Vice President Mike Pence re-enacts her swearing-in. Hide Caption 35 of 45 Photos: Former presidential candidate Elizabeth Warren Warren, her husband and dog Bailey attend an event in Manchester, New Hampshire, in January 2019. Warren had recently announced that she was forming an exploratory committee for the 2020 presidential race. Hide Caption 36 of 45 Photos: Former presidential candidate Elizabeth Warren Warren speaks in Columbia, South Carolina, in January 2019. Hide Caption 37 of 45 Photos: Former presidential candidate Elizabeth Warren Warren looks down at the crowd in Lawrence, Massachusetts, before formally announcing her presidential bid in February 2019. Hide Caption 38 of 45 Photos: Former presidential candidate Elizabeth Warren Warren answers questions at a town-hall event in Jackson, Mississippi, in March 2019. Hide Caption 39 of 45 Photos: Former presidential candidate Elizabeth Warren Warren makes a pinky promise with 8-year-old Sydney Hansen during a campaign stop in Peterborough, New Hampshire, in July 2019. Hide Caption 40 of 45 Photos: Former presidential candidate Elizabeth Warren US Sen. Bernie Sanders grabs Warren's hand during the CNN Democratic debates in July 2019. Sanders and Warren, two of the most progressive candidates in the field, were targeted early in their debate by their more moderate counterparts. Hide Caption 41 of 45 Photos: Former presidential candidate Elizabeth Warren Warren speaks at her Super Tuesday rally in Detroit in March 2020. Hide Caption 42 of 45 Photos: Former presidential candidate Elizabeth Warren Warren acknowledges supporters as she arrives to speak to the media outside her home in Cambridge, Massachusetts, in March 2020. She had just dropped out of the presidential race. Hide Caption 43 of 45 Photos: Former presidential candidate Elizabeth Warren Warren appears on "Saturday Night Live" with actress Kate McKinnon, playing Warren, in March 2020. "I wanted to put on my favorite outfit to thank you for all you've done in your lifetime," McKinnon said. "I'm not dead," Warren responded. "I'm just in the Senate." The two then said the show's famous catchphrase, "Live ... from New York! It's Saturday night!" Hide Caption 44 of 45 Photos: Former presidential candidate Elizabeth Warren Warren asks questions during a Senate committee hearing in June 2020. She was appearing via video conference because of the coronavirus pandemic. Hide Caption 45 of 45

Celebrities wrote big checks for Warren

As in past presidential elections, Hollywood celebrities are opening up their wallets for the Democratic candidates who hope to take on President Donald Trump next year. These are some of the A-listers in the entertainment industry who gave to Warren in the second quarter:

Amy Schumer (actor) : $5,600 (Schumer maxed out her contributions for both the primary and the general election)

: $5,600 (Schumer maxed out her contributions for both the primary and the general election) Scarlett Johansson (actor) : $2,800

: $2,800 Jeffrey Katzenberg (media executive) : $2,800

: $2,800 Bette Midler (actor) : $2,800

: $2,800 Shonda Rhimes (producer): $2,800

Warren has a whole lot of money to spend

Heading into the summer months -- often a period of slower political fundraising -- Warren has some $19.8 million cash on hand.

That war chest is only rivaled by the $27 million Sanders has in his coffers, and Buttigieg's $22.7 million cash on hand. For both Warren and Sanders, the money they were able to transfer over from existing accounts has proven to be hugely helpful: Warren transferred over more than $10 million from her Senate campaign account in the first quarter, while Sanders transferred over around $6 million from previous campaign accounts in the second quarter.