California Prop. 39 co-chair Tom Steyer with students at John Marshall High School in Los Angeles on Oct. 28. Marshall High has been approved for $1,836,072 of Prop. 39 funds for energy projects. (Damian Dovarganes/AP)

Tom Steyer, the billionaire climate activist, spent heavily to back environmentally friendly candidates for Congress in 2014.

But Tuesday’s election results produced a stunning disappointment, and a low return on his $70 million investment.

Many of the environmentally friendly candidates he backed most heavily­, such as Sen. Mark Udall in Colorado  and Rep. Bruce Braley in Iowa,­  were defeated — earning him a low “return on investment” score from the Sunlight Foundation, which ranks the major independent spending  groups that now dominate federal campaigns.

Steyer, who spent his own money launching NextGen Climate Action, had “little to show for his efforts,” the foundation’s staff concluded in the report  released Wednesday.

NextGen opposed Republicans in close races across the country but lost  major battles against Cory Gardner in Colorado and Joni Ernst in Iowa, both now Republican senators-elect. Both are considered likely to back  the Keystone Pipeline project, opposed by Steyer, major environmental  groups and the defeated Democratic candidates.

The Sunlight staff gave Steyer, who made his fortune as a hedge fund  investor, a 32 percent “return on investment” ranking, meaning that two  thirds of the money his organization spent went to support losing  candidates.

The results were similar for others aligned with the Democratic Party  battle plan: Senate Majority PAC, founded by former staffers to Sen. Harry Reid and fueled by donors including Steyer and Michael Bloomberg, also received a dismal return on investment score of 9 percent.

"Unprecedented levels of spending by conservative dark money groups fueled this historic and insurmountable electoral wave," said Ty Matsdorf, a spokesman for Senate Majority PAC, in an e-mailed statement. "In almost every Senate race, Republican outside groups outspent Democratic outside groups — nearly doubling overall Democratic spending."

Meanwhile, Republican Party-oriented groups that suffered similarly low ratings two years ago were flying high Wednesday, declaring themselves redeemed and offering to detail the ways in which their cash was  strategically well spent.

“The U.S. Chamber engaged early in the election cycle to ensure the  nomination of candidates who were not only pro-business, but also  willing to govern if elected,” said Chamber President Tom Donohue in a  statement issued late Tuesday.

Indeed, the chamber made a historic move this year to participate in  GOP primaries, backing Republicans the organization decided were best  aligned with mainstream business views.

The chamber received an 80 percent score from the Sunlight analysis, and  Crossroads received a 96 percent ranking in the study, which did not  include an analysis of primary spending.

“In 2014, conservatives turned the ship around, drubbing their liberal rivals in a year in which independent groups on both sides dropped unprecedented amounts of money,” wrote Sunlight analysts Jacob Fenton and Peter Olsen-Phillips. Two years ago, the Chamber of Commerce and Crossroads GPS had to endure after-action reports to determine what went wrong. Crossroads and the Chamber had together spent more than $124 million that cycle, and the Chamber had spent more than $24 million, much of it on losing Senate candidates. The White House and the Senate both remained under Democratic control that year.

This year’s record spending, like the records set in all recent cycles, raises question about what exactly these large expenditures buy.  At one level, a spending disparity suggests that money talked this cycle.

All told, Republicans and their allies are projected to have spent $1.75 billion, while Democrats and their allies spent $1.64 billion,  according to the Center for Responsive Politics, a nonpartisan research group, which compared Tuesday’s results against campaign finance data. The candidate who spent the most prevailed 94.2 percent of the time, the center found. The Senate figure is slightly lower at 81.8 percent.

But a close look suggests that spending is not determinative. There were several key Senate races, including those in Colorado and Arkansas, where Democrats and their allies outspent the GOP team, but still lost, the center reported.

The amounts of money spent by both sides were so vast, it is hard to know whether more money could have made a difference swaying voters overwhelmed with pitches from both sides. In North Carolina’s Senate race, for example, costs are expected to exceed $113 million, according to the center’s analysis. In that record-setting race, outside groups outspent the candidates themselves. Allies of GOP challenger Thom Tillis spent $37.2 million, compared with outside spending for Sen. Kay Hagan that totaled $33.1 million, also a healthy sum.

Although these numbers are calculated from filings with the Federal Election Commission, they likely understate the amount independent groups actually devoted to the race. For example, Americans for  Prosperity, a nonprofit that does not disclose its donors, undertook some activities, including airing so-called “issue ads,” that were not disclosed.

In 2012, a close analysis of individual races by The Washington Post  found no correlation between spending and election results.

The Center for Responsive Politics did not draw a conclusion about such a correlation this year. Instead, they concentrated on more disturbing  trends, including an overall decline in the actual numbers of donors  participating in a process that is increasingly dominated by a wealthy and  secretive group.

The real story of the election’s campaign finance  chapter was not which side had more resources, the organization’s  report said, but “that such a large chunk of the cost was paid for by a  small group of ultra-wealthy donors using outside groups.”