"They’ve bulldozed competition, used our private information for profit, and tilted the playing field against everyone else," Warren said at the time.
And this week, the Federal Trade Commission slapped Facebook with a $5 billion fine for its oversight on user privacy and the Department of Justice has opened up an investigation into big tech companies' alleged anti-competitive behaviors.
But the sweet power of paid placements on social media -- including strategic spending on digital platforms that curate deeply relevant and individually-targeted content for primary voters -- is critical for campaigns as they strive to build strong grassroots support in early states and in key geographic areas.
And in less than a month after Warren's declaration, her campaign paid Facebook and Google nearly a half million dollars for digital ad placement, including ones calling for dissolution of the very same tech giants. In two months, her online ad spending grew to $1 million. To date, the Massachusetts senator remains one of the largest patrons among the field of presidential hopefuls of big tech companies for ad buys -- spending at least $3 million on ad placements on various online platforms since January this year.
Sen. Bernie Sanders, I-Vt., who answered "yes, of course," when asked if he supports Warren's crusade against big tech, has spent $2.7 million running ads on Facebook and Google, and Sen. Kamala Harris, D-Calif., who said in an interview with CNN that the U.S. "should seriously take a look at" dismantling Facebook, has similarly spent $2.4 million on Facebook and Google ads.
Former Vice President Joe Biden, too, who said breaking up Facebook is "something we should take a really hard look at" in an interview with The Associated Press, has become one of the most aggressive online advertisers despite jumping into the presidential bid much later than his rivals, purchasing more than $3.4 million worth of digital ads since late April this year, according to ABC News' analysis of his campaign disclosure report.
"We are running a robust digital advertising operation to ensure we are putting our campaign in a position of strength to take on Donald Trump," Biden's campaign spokesperson Matt Hill told ABC News in a statement. "Meeting voters where they are on digital platforms is crucial for a modern presidential campaign and strategic investments in advertising will remain a priority."
In total, Democrats running for presidency in 2020 have spent nearly $28 million on online ads since January this year, according to Democratic digital firm Bully Pulpit's analysis of Facebook and Google ad data. In comparison, Trump's reelection campaign, back by the Republican National Committee's massive war chest, has run about $13 million worth of Facebook and Google ads so far this year.
South Bend, Indiana, Mayor Pete Buttigieg and Sen. Cory Booker, D-N.J. -- who have been fundraising among Silicon Valley power brokers -- have taken a more diplomatic stance, acknowledging the need for checks and balances on social media giants but stopping short of calling for break up of the companies. Buttigieg and Booker have spent $2.5 million and $2 million, respectively, on Facebook and Google ads so far.
And big spending on digital ads wasn't limited to candidates with big sums in their banks -- many of the lower-tier candidates too were also dishing out on online campaigns, so much so that some of them were burning through much of their campaign funds on digital operations, a costly effort to boost the number of donors so that they can qualify for the debates.
Sen. Michael Bennet, D-Colo., and former Housing and Urban Development Secretary Julián Castro burned through more than half of their total spending throughout the second quarter on digital ads, while Washington Gov. Jay Inslee and Sen. Kirsten Gillibrand, D-N.Y., spent about a third and a fourth of their funds, respectively, on digital ads.
"I really don't want to spend all my campaign money on Facebook right now trying to get unique donors," said Sen. Amy Klobuchar, D-Minn., whose presidential campaign has spent about $1.6 million on Facebook and Google ads so far this year.
Rep. Tulsi Gabbard, D-Hawaii, on Thursday, filed a $50 million lawsuit against Google, accusing the company of discriminating against her campaign and controlling public access to information by temporarily suspending her ad account without any explanation. Her campaign has spent a total of about $620,000 on Facebook and Google ads so far this year.
Google's spokeswoman Riva Sciuto told ABC News in a statement that the suspension of the Gabbard campaign's ad account was an automated process triggered by an unusual activity, and said that the account was restored shortly.
"We have automated systems that flag unusual activity on all advertiser accounts -- including large spending changes -- in order to prevent fraud and protect our customers," Scuito said. "In this case, our system triggered a suspension and the account was reinstated shortly thereafter. We are proud to offer ad products that help campaigns connect directly with voters, and we do so without bias toward any party or political ideology."
Concerns over the lack of oversight on social media giants have been brewing over the last couple years, following the revelations of Facebook's massive user privacy data breach -- as well as an extensive Russian disinformation campaign to influence the 2016 presidential election, an issue that was revisited during special counsel Robert Mueller's testimony on Wednesday. Several of the Democrats -- including Biden, Warren and Klobuchar -- have criticized social media giants, calling for transparency in online campaign ads, which are not bound by the same disclosure rules as political ads on television, radio and print news.
Facebook, Google and other online platforms since 2018 have started disclosing some information on sponsors behind political ads, but the Congress, the tech industry, and the regularly agencies have yet to find common ground on comprehensive and uniform way of disclosing the information.
"All eyes are on campaigns’ digital operations for a multitude of reasons -- it’s a scalable way to meet donor requirements for debates, and it’s an effective way to personally and authentically talk to supporters and prospective voters en masse -- and that’s just the start," Bully Pulpit Interactive Director Jane Hughes told ABC News.
"While candidates are right to call out foreign interference in our elections, it’s also true that hundreds of millions of Americans rely on tech platforms for their information and spend more time online than with any other medium," Hughes added. "This makes it a natural -– and critical -– place for candidates to talk to and with voters in a highly tailored, targeted way."
Facebook CEO Mark Zuckerberg, in an op-ed earlier this year, called for more government regulation on harmful content, election integrity, privacy and data portability, admitting that social media giants have "too much power over speech" and that "we shouldn't make so many important decisions about speech on our own," but Facebook's vice president for global affairs and communications Nick Clegg in another op-ed later that year pushed back against the calls for breaking up Facebook.
Zuckerberg, in an interview with ABC News' George Stephanopoulos earlier this year, said he is "confident" about the 2020 presidential election, saying Facebook has learned a lot since 2016 and is investing more on safety and security measures to protect the integrity of American elections.
But as the federal government revisits Facebook's past data breach incident and alleged monopolistic tendencies, 2020 Democrats' interest in the big tech industry is expected to continue.
"I think we need vigorous antitrust legislation in this country because you are seeing--you name the area, whether it's pharmaceuticals, whether it is Wall Street, whether it is high tech," Sanders said at a Washington Post event last month.