(CNN) House Republicans on Thursday signaled how they plan to fight back attempts by Democrats to obtain President Donald Trump's personal tax returns, describing the effort in a hearing as a "waste of time" and "weaponizing" the law to target a political foe.

Throughout a more than two-hour hearing on Capitol Hill, GOP lawmakers pressed tax historians and experts over whether a House tax-writing committee has the legal authority to request such confidential financial documents from the Treasury secretary, describing it as a clear violation of privacy of any individual American that would set a "dangerous precedent."

"Where does it end? What about the tax returns of the speaker? Political donors? There is no end in sight," said Rep. Mike Kelly of Pennsylvania, the top Republican on the House Ways and Means subcommittee panel, at the hearing. "Every single American has the right to privacy."

It was an argument that Republican lawmakers returned to repeatedly in reviewing a provision in the Democrats' sweeping ethics reform legislation -- H.R. 1—that requires future presidential candidates and the President to release 10 years of tax returns.

Thursday's hearing was a step aimed at helping Democrats bolster their case for why the American people need to see Trump's tax returns, arguing given his array of business dealings, including overseas, should be revealed to the public.

But it soon became the first real skirmish between Trump's defenders in Congress and newly empowered Democrats since the House changed hands last month.

"I welcome this time of examination," said Rep. John Lewis, a Georgia Democrat and chairman of the panel, channeling Richard Nixon. "People have got to know if their President is a crook."

Illinois Republican Rep. Darin LaHood blasted the effort by Democrats as a "waste of time and energy and resources" of the committee, arguing such a step was unprecedented especially while a sitting president was undergoing an independent investigation by the special counsel's office.

"I look at the legitimate purpose and the legal purpose and I don't see it," said LaHood. "I go back to what my colleagues said about weaponizing the tax code and we should all be concerned about that."

Since the early 1970s, most presidents have chosen to release their tax returns to the public for the years they serve in office and only while they hold office, which they are not required to do under the law. The practice began with Jimmy Carter, who ran and took office in the aftermath of President Richard Nixon's tax scandal and Watergate.

That tradition broke in 2016, when Donald Trump became the first major candidate to refuse, citing an ongoing audit.

Joe Thorndike, director of the Tax History Project, expressed concern that such a refusal could break a historical record that has lasted over four decades.

"I am concerned that it may be completely broken," said Thorndike, adding "Then we can't really rely on a tradition to get the job done."

Richard Neal, the chairman of the House Ways and Means Committee, has said he plans to request Trump's returns using IRS code 6103, a provision that Democrats say allows the chairman of the House Ways and Means committee to request Trump's tax returns, a move separate from the legislative debate on requiring future commanders in chief to release their records.

The law, which Democrats can invoke without Republican approval, states that the chairmen of the Senate Finance Committee and House Ways and Means committee each have the power to request taxpayer information and states that "the secretary shall furnish such committee with any return or return information specified in such request."

The decision of how to handle a request for Trump's returns will fall to Treasury Secretary Steven Mnuchin, one of the President's closest confidants and earliest backers. A Treasury spokesperson said Mnuchin would review any request for the President's tax returns with his general counsel to determine if they are required under law.

Some of the witnesses -- a crew of tax and ethics experts -- have urged Congress to demand them, arguing that it would provide answers to whether the President, who has maintained ownership of his business, is benefiting from public office

"I don't see any wiggle room for the Treasury secretary to refuse the request," said George Yin, a professor at the University of Virginia School of Law and former chief of staff for the Joint Committee on Taxation, adding it would be "unprecedented" for the secretary to refuse.

One looming question is whether the committee has the legal authority to disclose the President's tax returns upon receipt -- a topic Yin and Ken Kies, the managing director of the Federal Policy Group sparred over throughout the hearing, with each taking a contradictory view.

Trump's lawyers have already threatened a court fight over the release of the returns, and Democrats on Capitol Hill anticipate that Treasury will take its time in reviewing any request.

In January, Neal told CNN that he is "judiciously" pursuing Trump's tax returns . "I think the idea here is to avoid the emotion of the moment and make sure that the product stands up under critical analysis," he said. "And it will."

Republicans have dismissed the Democratic effort as a partisan witch hunt.

"I would expect the President to use every legal means he can to keep that from happening. I don't know what those legal means are, I just would expect him to use every legal means," said Senate Finance Committee Chairman Chuck Grassley, an Iowa Republican. "I thought we learned a lesson about the politicization of the IRS when Nixon was President and that is why 6103 was passed, so what are the Democrats doing trying to use the IRS as a political tool? It's just as wrong (as) if Nixon were doing it."

On Wednesday, House Minority Leader Kevin McCarthy said he views the House Ways and Means Committee's ability to seek Trump's tax returns as "political."

"I think Ways and Means should focus their time making sure of how strong this economy is today, of how we can make it stronger," said McCarthy, a California Republican. "I think that's the focus of the American people would like to see going forward, and that's the focus we'd have as well."