WASHINGTON (AP) -- Campaign money from shadowy sources is back this election. More than $4 million of it channeled to outside groups helping presidential candidates has come from unknown or masked donors.
Super political action committees, or super PACs, helping White House hopefuls like Marco Rubio and Hillary Clinton received big checks recently from obscure corporations or from nonprofits that don't have to disclose their donors' names.
A super PAC backing Rubio, a Republican senator from Florida, benefited from companies with spectral names like "IGX LLC" ($500,000) and "TMCV #2 LLC" ($90,000). The Associated Press traced IGX to a New York investor, and the other to an Idaho billionaire.
Meanwhile, Democratic-leaning American Bridge 21st Century reported more than $1.5 million from its affiliated nonprofit, which doesn't have to name its donors. American Bridge, which said it used the money to pay for shared expenses like rent and staff, was founded by Clinton supporter David Brock.
The contributions are a reminder of federal court decisions in recent years, like Citizens United, that loosened prior restrictions in campaign finance laws. That has made it difficult at times to tell who's really backing candidates — and what favors or influence could be owed should they get elected.
The AP counted more than two dozen groups that each gave at least $50,000 to presidential-aligned super PACs during the last three months of 2015. At least half of those were unrecognizable names like family trusts, real estate holdings or firms that were far from household brands.
The AP over several days pieced together who was behind some of the donations by analyzing more than 80 million campaign finance records, property tax documents and other public records.
Opaque contributions aren't new: In 2011, a once-mysterious group gave $1 million to a super PAC supporting then-GOP presidential candidate Mitt Romney. The group was formed by an executive at Romney's old company, and that co-worker ultimately acknowledged he was behind the contribution.
But this time, no White House incumbent likely means more money to go around, especially during a contentious primary season. Much of the super PAC money so far has paid for pricey political ads, among other expenses.
The largest, obfuscated super PAC donation was IGX's $500,000, paid to the Rubio-aligned Conservative Solutions PAC. The AP discovered the contribution came from self-described investor and IGX owner Andrew Duncan of Brooklyn, New York, whose firm was listed in a prior donation to Rubio.
Duncan helped host a Rubio fundraiser last October, less than two weeks before the $500,000 donation. Duncan is listed separately on Rubio's campaign website as pledging to "buy Marco a plane ticket." At least half of his $40,000 in donations since 2012 went to Democratic Party candidates, including a $2,700 donation last May to Clinton's campaign.
Rubio has said it's important for people to know the source of political money.
"I think that as long as people know who is giving you money, and why it is, people can make judgments on why you are doing what you are doing," Rubio said at a September campaign stop in New Hampshire.
Duncan, who said he worked as a technology executive and has invested in several film productions, acknowledged he was the source of the super PAC donation in emails Tuesday to the AP. Duncan, who funds human-rights efforts in China, said he admired Rubio's work on the issue and had used IGX to mask the donation because he was worried about reprisals.
Even frequent contributors whose names appear elsewhere in Federal Election Commission data donated through an alphabet soup of companies.
One conservative super PAC donor, Frank VanderSloot from Idaho, gave $150,000 under his own name to Conservative Solutions PAC. Yet records indicate two companies tied to him gave an additional $175,000 to the same PAC, which has so far spent $14.8 million in ads this election, according to political ad-tracker Kantar Media.
That firm, TMCV #2 LLC, owns a corporate development property in Utah, whose property records are shared with the VanderSloot-owned Riverbend Ranch in Idaho Falls, Idaho. And NG Montana LLC, which also contributed $85,000 to Conservative Solutions, lists the same Idaho address in federal campaign finance records.
In an interview, VanderSloot confirmed he was behind the contributions but denied he was trying to hide money. He said the super PAC called him in late December requesting more donations, and "that's where we had cash at that moment."
"Just wait until this year," VanderSloot said. "We're going to send bucketloads. This was teaspoons."
A super PAC supporting Republican Ohio Gov. John Kasich also benefited from New York real estate developer Peter S. Kalikow, the former publisher of the New York Post. He gave $125,000 through HJK LLC, a company registered to Kalikow's firm HJ Kalikow and Co.
Spokesman Martin McLaughlin said HJK is just one way Kalikow chooses to make donations.
"It's not a mystery that Peter Kalikow supports Republican candidates," he said.