'Dark money,' used by both parties, featured in $100 million pro-Biden ad blitz

As an influx of eleventh-hour outside money pours in to boost both presidential candidates, so-called "dark money" groups, which don't have to disclose the source of their funding, and a host of Silicon Valley executives are quietly fueling a massive last-minute ad campaign in support of Democratic presidential nominee Joe Biden.

Future Forward, the super PAC fronting the effort, has mostly remained under the radar until late September, when it began rolling out a six-figure television ad blitz in support of the former vice president. The group is now on track to spend more than $108 million on pro-Biden television ads across the country in the final five weeks of the presidential race, becoming the single biggest political ad spender entering the home stretch of the 2020 election, according to ad placement data.

Super PACs like Future Forward are required to disclose their donors to the Federal Election Commission, but the group reported nearly half of the $74 million it has brought in through mid-October as coming from politically active nonprofits, or so-called "dark money" groups that are not required to disclose their donors to the FEC the same way as PACs and super PACs do -- a tactic used increasingly frequently to mask who's funding political campaigns. The rest of the money that's been reported to the FEC is from a handful of Silicon Valley influencers and major Democratic donors.

In early September, a similar last-minute boost for President Donald Trump popped up as the president repeatedly trailed his Democratic challenger in fundraising and spending. The super PAC, called Preserve America, backed by big-name GOP donors like casino mogul Sheldon Adelson, has since aired and reserved whopping $82 million worth of television ads in support of Trump, but it has not reported receiving contributions from dark money groups and instead reported receiving most of its funding -- $75 million -- from Adelson and his wife.

Future Forward's move underscores the critical role that controversial "dark money" has played in recent elections and the increasing use of that money to make a push as campaigns enter the home stretch.

During the 2016 cycle, dark money groups spent at least $66.8 million on the presidential election, with more than twice the amount spent to benefit Republicans than Democrats, according to data from the Center for Responsive Politics, though the murky nature of dark money spending disclosure makes it difficult to gauge the full picture.

The last-minute boost from Future Forward has provided critical additional support for Biden and the Democrats in some of the key battleground states like Pennsylvania, Michigan and Wisconsin, as the campaign and the party invest heavily in Florida and North Carolina, ad data from media research firm Kantar/CMAG shows.

Future Forward, led by Chauncey McLean, the Democratic Party’s director of media tracking in 2012, has been around since 2018 but has only begun making significant moves late this election cycle.

The group has quickly risen to become one of the biggest players in the presidential race, on par with longtime Democratic super PAC Priorities USA Action's operation, which has already spent $130 million so far this election cycle, as well as billionaire Michael Bloomberg's pledge to spend $100 million toward helping Biden win Florida in November.

60,000 spots

According to CMAG's ad data, Future Forward has already aired 14 different ads over nearly 60,000 spots in the past few weeks, many of them zeroing in on the state of the coronavirus pandemic.

Several ads feature medical experts and healthcare workers criticizing the president's response to the public health crisis, such as failing to make the right moves early in the pandemic, contrasting it to Biden's plan to ramp up testing operation.Those ads also highlighted Biden's plan to offer free vaccines. Back in September, Paul Mango, deputy chief of staff for policy at the Department of Health Human Services said the administration's goal is that "no American has to pay a single dime out of pocket to get a vaccine," but on Tuesday, the government is reportedly preparing to provide "early vaccines" for those covered by Medicare and Medicaid.

A few ads also criticize Trump and the Republicans' move to try to repeal the Affordable Care Act, saying the president is trying to kick 23 million Americans off of health insurance during the pandemic and to repeal protections for pre-existing conditions. The president has repeatedly committed to preserve protections for those with pre-existing conditions, even signing an executive order promising to do so, but health experts say the president has done little to actually protect them, let alone put forward an actual alternative proposal to the Affordable Care Act.

One of Future Forward's most recent ads features a mash-up of Trump speaking, saying that "one day," the virus will "disappear" like a "miracle," that the president has "always wanted to play it down" -- and that he still likes playing it down -- and that he told his team to "slow the testing down." The president has defended his efforts to downplay the pandemic saying he wanted to avoid panicking the public, and Trump's advisers have said the president was joking when he said he wanted to slow down the testing, though Trump later said he "[doesn't] kid."

In another ad, an unknown narrator calls the sitting president erratic, subsequently playing Trump's own voice saying he's has "five different strategies that he can change any moment."

Silicon Valley heavily invested

Future Forward's disclosure filings offer a glimpse of some of the donors -- mostly a rolodex of Silicon Valley influencers that are increasingly becoming a major part of the Democratic mega-donorslist.

Facebook co-founder Dustin Moskovitz has put in at least $22 million of his money into Future Forward. Longtime Google CEO Eric Schmidt also gave more than $2.5 million, while communications platform Twilio's chief Jeff Lawson and his wife Erica Lawson, a physician at University of California-San Francisco, also together gave $6 million, according to the FEC filings.

Kathryn Murdoch, daughter-in-law of billionaire media mogul Rupert Murdoch, who, along with her husband James, split from the Murdoch family to come out in support of Biden earlier this summer, also gave $540,000.

Several of the Future Forward donors have also given more than $600,000 to Biden's campaign and the Democratic Party's joint fundraising committee, past FEC reports filed by Biden's committees show.

Funding a mystery

But a good chunk of Future Forward's money is coming from is still shrouded in mystery.

Future Forward, which reports to the FEC under the name of FF PAC, has so far reported bringing in $74 million from June last year through mid-October, $66 million of which came just since September, disclosure reports filed to the FEC show.

But at least $29.3 million of that, according to the filings, is from its own nonprofit arm Future Forward USA Action.Organizations across the spectrum like Future Forward often have a super PAC that is fully dedicated to political activities and are required to report all their fundraising and spending to the FEC, and a social welfare nonprofit arm, also known as 501(c)(4) group or politically active nonprofit, which are allowed to engage in some political activities and contribute to political organizations but are not required to disclose all of their donors and spending. Landmark Supreme Court case Citizens United from 2010 has allowed super PACs to bring in an unlimited amount of money from individuals and entities like politically active nonprofits.

Another $3.9 million of Future Forward's money is also shrouded in mystery, because it's from Sixteen Thirty Fund, another prominent Democratic politically-active nonprofit that has funneled tens of millions into liberal groups, the reports show.

Sixteen Thirty Fund, which does not have to report funding because it is a politically-active nonprofit, is led by veteran Democratic operative Eric Kessler, a Clinton administration adviser.

Future Forward and Sixteen Thirty Fund did not immediately respond to ABC News' request for comment.

The Biden campaign did not immediately respond to ABC News' request for comment.

Dark money increasingly common

Donations and spending from such non-disclosing political groups are often called "dark money" or "gray money" because the source of funding is not revealed to the public unless it's disclosed voluntarily by the groups or as part of spending reports from other groups that are required to disclose their expenditures that have given to them.

The practice of super PACs circumventing donor disclosure rules by receiving money from dark money groups has become increasingly common, including major pro-Trump super PAC America First Action, which has received more than $15 million so far this year from its affiliated non-disclosing nonprofit America First Policies (a smaller fraction of its $129 million haul this year than Future Forward).

The practice is also common on the congressional side. One Nation, a conservative political nonprofit that does not disclose its donors, has given nearly $22 million over the years to pro-Senate GOP leadership super PAC, Senate Leadership Fund, FEC filings show. On the Democratic side, Majority Forward and House Majority Forward, non-disclosing liberal political nonprofits, have given more than $12 million to Senate Majority PAC and House Majority PAC, super PACs linked to the Senate and House Democratic leadership, according to FEC reports.

While numerous groups have used this method to mask their source of funding over the years, Brendan Fischer, the federal reforms director at government ethics group Campaign Legal Center said the sheer level of dark money that is fueling this massive last-minute operation is unprecedented.

"I can't recall such a huge infusion of dark money from an affiliated [nonprofit] in the final stretch of an election," Fischer said.

"This is an increasingly common way that these groups are able to add an extra layer of insulation between the ultimate source of funding and the groups that are doing the spending to influence elections," Anna Massoglia, a political nonprofit expert at the Center for Responsive Politics, told ABC News.

"Political committees that are really required disclose their donors have taken a record-breaking amount of dark money contributions during the 2020 election cycle, with hundreds of millions of dollars flowing from dark money groups into political contributions to contributions to political committees," Massoglia added.