Newly elected members of Congress benefited from millions of dollars indirectly tied to party leaders in Washington. But much of that money was spent on ads that appeared to be from local groups, according to a study released Thursday.

The tactic is legal, thanks to campaign finance laws that have not been updated since the dawn of the digital age and Supreme Court rulings that have struck down limits on money in politics. But such strategies, laid out in the nonpartisan Campaign Legal Center’s “Dodging Disclosure” report, represent the acceleration of “big money trends” that have given deep-pocketed groups outsize influence over elections and made the 2018 midterms the most expensive in American history, the report said.

Candidates elected with millions of dollars of outside spending “may very well be accountable to those big spenders,” said Brendan Fischer, one of the authors of the report. “Identifying that potential corruption and whether that candidate would indeed be accountable to those large donors is only possible if we know who those donors are.”

Such developments don’t sync with indications that voters want more transparency and accountability in their government, including the large number of Democratic candidates who vowed to reject money tied to business interests and local anti-corruption ballot initiatives that passed in cities and states across the country, the report concluded. 

The Campaign Legal Center is a nonprofit focused on campaign finance and elections. 

At least $8.9 billion was spent on advertising for the midterms, according to preliminary estimates from the media research and consulting firm Borrell Associates that were cited in the report. Of that, hundreds of millions of dollars came from super PACs and so-called dark money groups, funded mostly by “a handful of megadonors,” the report found.

Such groups have funneled staggering amounts into elections since the landmark 2010 Citizens United ruling that made it easier for corporations and labor unions to spend unlimited amounts of money on political campaigns. 

But 2018 was the first year that unlimited spending from nationally focused, party-aligned super PACs surpassed that by party committees such as the National Republican Congressional Committee or the Democratic Congressional Campaign Committee, which are subject to strict contribution limits, the report found.

Congressional Leadership Fund, which is aligned with outgoing Speaker Paul D. Ryan and House GOP leadership, spent the most at $137.5 million, the report found. The second-highest spender was Senate Majority PAC, tied to Senate Democrats led by Charles E. Schumer, which spent $112.8 million. Senate Leadership Fund, associated with Senate Majority Leader Mitch McConnell and the chamber’s top Republicans, came in third at $95 million. The parties’ House congressional committees took the fourth and fifth spots.

In turn, those groups found new ways to “disguise” their spending by taking advantage of gaps in federal disclosure requirements and lax federal enforcement, the report found. 

Examples include “mysterious” super PACs that appeared in several races after the last pre-Election Day deadlines to report the sources of their funding — meaning voters would not get that information until weeks after ballots had been cast. 

“The political operatives running these super PACs likely calculated that voters would respond more favorably to messages from a group that appeared to have local ties than from national super PACs and the D.C. political establishment,” Fischer said. 

The report cited a group called the “Mountain Families PAC,” which spent $1.3 million in the West Virginia’s Republican Senate primary, a high stakes race for party leaders seeking a candidate who could unseat vulnerable Democratic incumbent Joe Manchin III.  

That group avoided disclosing until after Election Day that most of its funding came from the Senate Leadership Fund, and it did not receive any money from West Virginia.

Groups aligned with Democrats used similar tactics, the report found. In one example, the “Duty and Country PAC” spent around $1.8 million in the West Virginia Republican primary. It filed reports after the election showing that it was funded by “a handful of Democratic donors,” the report found. 

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Groups also shrouded their true identities in digital ads, which are exempt from Federal Election Commission disclaimer requirements that apply to other media. The sources of many of those ads were revealed in the summer when companies such as Facebook introduced their own requirements that political ads had to include disclaimers showing funding sources.

Examples include paid ads that ran throughout the year from a seemingly nonpartisan Facebook page called “Hoosier Country,” attacking Indiana Republican Senate nominee Mike Braun. It was later revealed that the advertisements were paid for by the Democrat-aligned Senate Majority PAC and Priorities USA Action.

Super PACs can funnel unlimited amounts of money from corporations, unions, associations and individuals into campaigns, so long as they don’t coordinate with the candidates they benefit, according to a 2010 federal court ruling. So-called dark money refers to political spending from undisclosed sources, thanks to gaps in campaign finance laws. 

The Campaign Legal Center’s Fischer said there are “relatively easy fixes” to many of the problems the report uncovered.

Candidate committees are already given 48 hours to report all donations of $1,000 or more they receive in the weeks before Election Day. Congress could extend those requirements to super PACs, he said. The FEC could also require digital advertisements to follow the same disclosure requirements as other types of ads. 

“If Congress and the FEC do not act,” he said, “the trends we saw in 2018 will only return with greater force in 2020 and beyond.”