Opponents of the Obama administration's effort to normalize relations with Cuba and some ethics watchdogs are questioning the lack of transparency behind a million-dollar advocacy campaign that pushed for the historic thaw.

Two articles — one that was published in the September/October issue of Mother Jones, and another in the January edition of The Nation — detail the back-channel negotiations and behind-the-scenes lobbying campaign leading up to President Obama's December rapprochement to change five decades of U.S. policy and renew ties with the island nation.

Both reports also give a Denver-based progressive government relations firm, the Trimpa Group, credit for an elaborate behind-the-scenes lobbying campaign that helped press the administration into action on Cuba.

But there are no lobbying disclosure records on Congress's searchable database on the Trimpa Group's Cuba campaign, according to a Washington Examiner review of the files.

For two years leading up to the Obama administration's rapprochement with Cuba, opponents of the policy heard rumors of various lobbying and public advocacy campaigns taking place on the issue, but could never track the funds or identify who was orchestrating it.

"All we want is a level playing field," said Jason Poblete, a lawyer and registered lobbyist representing 10 American families pressing the Obama administration to recover billions of dollars in seized assets the Castro regime took after the country's 1959 revolution.

"Americans who were injured by the communist regime in Cuba deserve justice," he said. "The U.S. government and elected leaders need to speak for them and defend their interests."

Several ethics watchdogs interviewed for this article say lobbying disclosure is based on self-reporting, and there are so many loopholes and so little enforcement that it's difficult if nearly impossible to tell if firms are breaking the spirit or the letter of the disclosure law.

Meredith McGehee, policy director of the Campaign Legal Center, said it's conceivable that the Trimpa Group did nothing legally wrong in failing to file lobbying disclosure reports. But she also said that doesn't make it right.

"I think most Americans would be shocked to find out that a million-dollar campaign could be run to effect Washington policy and it can go essentially unreported in the official channels," she told the Examiner.

John Wonderlich, the policy director of the Sunlight Foundation, a non-partisan nonprofit dedicated to making government more transparent and accountable, agrees with McGehee. He said firms or trade associations that lead the lobbying campaigns often are not required to file lobbying disclosure reports because they are doing the strategic planning and are not involved in contacting members of Congress or administration officials directly.

Ted Trimpa is CEO of the Trimpa Group, and he was dubbed "Colorado's answer to Karl Rove" by The Atlantic. Trimpa got his start in politics working for former Kansas centrist GOP Sen. Nancy Kassebaum. In an email, Trimpa referred the Examiner's inquiry about the lack of lobbying disclosure reports for the firm's Cuba activities to James Williams.

Williams served as director of public policy at the Trimpa Group and worked on the Cuba campaign before leaving in early May to become president of a 501(c)4 called Engage Cuba, which is focused on lifting the trade and travel restrictions between the two countries.

Williams didn't return several calls and emails from the Examiner. But he was still sending out Cuba-related tweets on Friday, touting stories in the Washington Post about an arugula farmer in Cuba starting a culinary revolution and another from the Boston Globe on Cuba opening its doors to U.S. travelers.

An automatic reply to Williams' Trimpa Group email account lets people know about his transition to heading Engage Cuba after "four incredible years" at Trimpa.

A separate firm, Fierce Government Relations, filed one lobbying disclosure report for Engage Cuba this year, listing $70,000 in income for its lobbying for the second quarter of this year.

That sum, however, doesn't cover any income the Trimpa Group received for its Cuba work this year or in 2014, leading up Obama's Cuba policy announcement in December.

The Nation article from January, which the Trimpa Group posted on its website, describes Trimpa's lobbying role in the Cuba campaign as a critical one that flew mostly under the radar.

"From the outside, leading advocacy groups, such as the Washington Office on Latin America and the Center for Democracy in the Americas, helped sustain public attention; and the Trimpa Group, a strategic philanthropic agency, played an important behind-the-scenes role in creative lobbying," the Nation reported in the January article.

Mother Jones went even further in detailing the Trimpa Group's role. In an article in its latest issue titled "Cuba Confidential: Inside the Crazy Back-Channel Negotiations that Revolutionized our Relationship with Cuba," the story praised the Trimpa Group for pulling out "all the stops" in its campaign to make renewing ties with the Castro regime a top Obama priority.

Still, experts on the rules that govern lobbying disclosure reports say there are so many loopholes and reporting requirements are so seldomly enforced that it's nearly impossible to know whether Trimpa should have filed without information about whether they contacted or had meetings with administration officials or congressional offices.

In addition, if the person working on the Cuba campaign did not spend at least 20 percent of their time on that particular client, they could also avoid filing lobbying reports on their activity and funds spent on it.

"Unfortunately, it's kind of hard to know what isn't reported because you can't see that," said Sarah Bryner, research director for the Center for Responsive Politics, a nonprofit that tracks political spending and lobbying disclosure. "If they were just doing public relations, they also wouldn't have to file."

The Mother Jones article lays out exactly how Trimpa was hired to do the Cuba work, and suggests that the firm's campaign involved direct contact with both administration officials and members of Congress, work that may have required disclosure.

The article says the Trimpa team "met with key foreign policy officials" and conducted a three-month survey of the political landscape, reporting that the "highest level of decision makers within the Obama administration" wanted change and that "they just needed political reinforcement to push for it."

The group, according to the article, also counseled a wealthy Cuban-American, Patty Ebrahimi, who was financing the Trimpa campaign and had agreed to spend at least $1 million on advocating for a change for Cuba, to make donations to key political figures, such as Senate Majority Leader Harry Reid, D-Nev., and Sen. Dick Durbin, D-Ill. These donations were intended to gain access and "be in the room," the article said, quoting Trimpa's strategic plan.

In addition, the lobby shop hired Luis Miranda, who recently left his position as Obama's director of Hispanic media, and sought the blessing of Jim Messina, Obama's then-deputy chief of staff, to launch a public campaign promoting a change in Cuba policy, the article states.

The Trimpa Group told Obama administration officials there would be no "political blowback" for Democrats in Florida if the president changed Cuba policy and financed a series of polls to bolster the argument.

Wonderlich said he found it "odd" that Trimpa Group posted The Nation article touting its "creative lobbying" work on Cuba on its website but did not file lobbying reports.

"It is odd — there's a question about whether they're trying to get away with something or it's just an error," he said, also noting the possibility that Williams did not spend at least 20 percent of his time on the Cuba issue to trigger the filing requirement.