The new Democratic House majority is making campaign finance overhaul a central part of its sweeping good governance agenda, capitalizing on an anti-money-in-politics platform that many candidates rode to Congress.

But when it comes to the big-money world of outside spending, over which candidates have little control, it appears that liberal groups had a banner year in 2018.

For the first time since the 2010 Citizens United Supreme Court decision, which struck down campaign spending limitations for corporations and unions, liberal “dark money” groups outspent conservative groups, according to a new report from Issue One that analyzed data from the Center for Responsive Politics.

Dark money groups spent $150 million in the 2018 midterms. And unlike super PACs, which must disclose their donors to the Federal Election Commission, these politically active nonprofits are not required to do so.

Liberal groups spent about 54 percent of that total in the 2018 cycle, with conservative groups only spending 31 percent. Nonpartisan or bipartisan groups made up the remaining 15 percent. The liberal dominance is a marked shift. In 2016, conservative groups that don’t have to disclose their donors outspent liberal groups 4-to-1, according to Issue One.