When Brett Kavanaugh testified in front of the Senate Judiciary Committee last month, he launched an attack on what he called the “millions of dollars in money from outside left-wing opposition groups” spent fighting his nomination. And when Maine Republican Sen. Susan Collins announced her support for Kavanaugh, she called out the “interest groups” that, she said, “have also spent an unprecedented amount of dark money opposing this nomination.”

Their condemnations of the Supreme Court nomination process being increasingly politicized were accurate. Groups opposed to Kavanaugh did spend millions in an effort to keep him off the bench. But Kavanaugh and Collins ignored one fact: Organizations that supported the judge spent even more on the confirmation fight, watchdog groups found.

While little information is publicly available about digital advertising, a massive and ever-growing market, groups supporting Kavanaugh did spend at least $7.3 million on TV ads alone, said Douglas Keith, counsel at Brennan Center for Justice, which has tracked spending around Kavanaugh’s nomination. In contrast, organizations opposed to the now-justice spent at least $2.9 million in TV ads against him between June and early October.

“In terms of the totals that we’ve seen disclosed, we’ve seen a lot more spending on the conservative side,” said Anna Massoglia, who researches dark money at the nonpartisan Center for Responsive Politics. “The side that was supporting Justice Kavanaugh was by far millions of dollars more.”

Neither of the Brennan Center’s estimates include the cost of production or commission; instead, they are based solely on the cost of air time on national cable and broadcast. They also don’t include any ads that might’ve aired on local cable, where ads are frequently bought for potential state Supreme Court justices.

“We didn’t have any hard data as to how much had actually been spent. And because of the nature of this spending, not only does the public not know the true source of the money, they didn’t even have any sense of who’s spending,” Keith said. Plus, he added, “There is no great resource for tracking the social media spending.”

Take the Judicial Crisis Network, Kavanaugh’s greatest conservative cheerleader in advertising. Like all so-called “dark money” groups, it does not disclose the source of its donations. The group spent at least $3.9 million on TV ads in favor of his confirmation, the Brennan Center found, but it’s unclear how much money it spent on digital ads.

While a search of Facebook’s Ad Archive turns up several dozen ad buys by the Judicial Crisis Network, each comes with a range of potential costs. An ad that ran in late September and early October — which called the allegations against Kavanaugh “one of the most calculated, shameful political-smear campaigns in our nation's history” — left between 100,000 and 200,000 impressions and cost between $1,000 and $5,000. That’s a vast gulf, particularly when multiplied across the dozens, if not hundreds, of Facebook ads run by the Judicial Crisis Network.

“Facebook requires information reported about the ad buyer but not necessarily much more than a paid for disclaimer, and that can be not much more than a very innocuous group name,” Massoglia said. Several groups that bought ads in the Kavanaugh fight, she said, appeared to exist only as Facebook pages. They often had names that began with phrases like “Americans For” or “Justice For.”

“There’s a lot of at least groups or coalitions that aren’t necessarily — they don’t exist as their own independent 501(c)(4), or nonprofit, or political committee,” Massoglia went on. “They just exist.”

All this murkiness also makes it difficult to track whether Kavanuagh’s confirmation cost more than that of Justice Neil Gorsuch, President Donald Trump’s first nominee to the high court, in early 2017. “We weren’t able to track it as well then because the Facebook political Ad Archive wasn’t around then,” Massogolia explained. “Before that, digital ads were just even more of a black hole.”

Such opacity isn’t just the purview of the pro-Kavanaugh camp. Judging by publicly available data, liberal groups did spend an unprecedented amount of money fighting Kavanaugh’s nomination, Massoglia said. That’s in large part thanks to Demand Justice, another dark money group that invested at least $1.1 million on TV ads opposing Kavanaugh, according to the Brennan Center.

Recently established as the left’s version of the Judicial Crisis Network, Demand Justice is perhaps even more shadowy than its counterpart. As an unincorporated entity, it doesn’t file tax returns or incorporation records.

“By and large, the groups that spent around this fight have no obligation to disclose their donors,” Keith said. “It makes it difficult for senators to assess the actual level of support for a nominee. It makes it difficult for voters to consider the arguments that are being put in front of them.”

He added, “In my view, it harms the nomination process by making it such that the loudest voices in it are the least transparent.”

Kavanaugh may have already ascended to the nation’s highest court, but ads invoking his name are still running: On Tuesday, the Judicial Crisis Network announced it was starting a “six-figure TV and digital ad campaign” in support of Collins.