The influence of “dark money” in American politics that allows billionaires to fund political campaigns through third-party groups without disclosing their involvement was put under the spotlight at a congressional hearing on Thursday, as Democrats use their newfound majority to crank up a sweeping new anti-corruption measure.

In the first hearing on the bill, known as HR1, the House administration committee examined how undisclosed donations from some of the country’s richest individuals is distorting they way politicians are elected.

“The mechanics of our democracy - access to voting, running for office, holding government accountable - have undergone radical changes in recent years,” Congresswoman Zoe Lofgren, the committee’s chairwoman, said while commencing the hearing.

She added: “These changes have tended to restrict the rights of eligible voters. It has made the voices of the wealthy and powerful so loud that they can drown out the voices of ordinary people.”

The committee heard from a range of election experts, as well as from civil rights activists, who illuminated the impact of such “dark money” on the lives of ordinary people.

A key example of the corrosive influence of secret political funding presented before the committee was the John Doe Files, the vast tranche of documents leaked to the Guardian in 2016 and posted in their entirety on the Guardian website. The 1,500 pages of material exposed how big corporations and some of the wealthiest rightwing donors in the US used their fortunes to prop up prominent politicians, in some cases going on to extract political favors in return.

Peter Earle, one of the panelists, was poised to appear before the committee later in the hearing to detail the revelations of the John Doe Files. A civil rights trial lawyer in Milwaukee, Earle has been suing the historic manufacturers of lead paint in a long-standing case designed to secure compensation for poisoned children as well as to generate funds needed to remove still existing toxic paint from hundreds of thousands of homes across the US.

“It is indeed a sad day for our democracy when a rich and powerful corporate CEO can deprive innocent victims of lead poisoning their day in court just because he could afford to secretly donate huge amounts of money to greedy and ruthless politicians,” Earle will say, according to a copy of his written testimony.

“The only reason that this story is publicly known is because years after the secret six- figure donation and subsequent sweetheart legislation, a trove of previously secret documents was leaked to the Guardian newspaper by a valiant whistleblower.”

The Guardian’s documents revealed that the late owner of one of the largest historic makers of lead paint, NL Industries, had donated $750,000 to a third-party group in Wisconsin that was heavily involved in helping the state’s then governor Scott Walker fight a recall election. As the money was passed through a group, the identity of the donor, NL Industries’ owner Harold Simmons, remained secret until the Guardian exposed it.

That meant that nobody was able to join the dots when, soon after Walker won the election, the Republican-controlled legislature in Wisconsin changed state law. Under the rule change, it became much more difficult for victims of lead paint poisoning, most of them children, to sue NL Industries and other former lead paint manufacturers for the damage inflicted on them.

Concern about the pervasive influence of undisclosed political donations by corporations and the super-rich has become a red hot issue, particularly among the new intake of young Democratic Congress members swept in by November’s mid-term elections. The “corruption game” played by Alexandria Ocasio-Cortez before the House Oversight committee in which she denounced campaign finance controls – or the lack of them – this week became the most viewed video of a politician’s speech ever posted on Twitter.

In it she said: “We have a system that is fundamentally broken.”

The Democratic party has chosen to mark its renewed dominance in the House of Representatives following the November elections by putting reform of America’s stricken democracy at the top of its agenda. HR1, known as the For The People Act, includes strong provisions designed to combat corruption by forcing all organizations involved in political activity, including so-called “social welfare” groups, to disclose large donors.

The bill is likely to be put to a House vote next month and is assured of passage through overwhelming Democratic support. It is almost certain to flounder, however, in the Republican-controlled Senate, given the virulent opposition from the party.

Mary Bottari, a researcher with the watchdog on money and politics, the Center for Media and Democracy, said Wisconsin should be seen as a cautionary tale for the nation. “Billionaires give huge amounts to aid politicians but because they gave it to a third-party group the public would never know.”

Many senior figures in the current Republican party and Trump administration appear in the John Doe Files. Trump himself has a walk-on part: the leaked documents disclosed that he made a donation of $15,000 following a personal visit from Scott Walker to Trump Tower in New York.

Another who makes an appearance in the documents is Nick Ayers, who has just stepped down as chief of staff to the vice president, Mike Pence. He has reportedly left the White House for a senior role in a super Pac that will be channeling money from big donors to Trump’s 2020 re-election campaign.

Also prominent at Thursday’s hearing was the issue of voting rights and efforts to restrict access to the polls that are predominantly aimed at people of color and students.

“The promise of this country is that every person has a voice and every person out to be counted,” Chiraag Bains, the director of legal strategies at the public policy organization Demos, told the panel. “Our history has been one of struggle to make that promise a reality.”