WASHINGTON — Republicans warned Thursday that if Democrats start to go after the president's tax returns it will "open a Pandora's Box" and accused Democrats of "weaponizing tax laws to attack a political foe."

The Ways and Means Oversight Subcommittee held a hearing on presidential and vice presidential release of tax returns Thursday afternoon. It was the first official step the Democratic-led House took towards trying to obtain Trump's tax returns, though a modest one.

Thursday's hearing was not specific to the president's taxes. Instead, it was billed as a hearing on a provision in a large piece of Democratic legislation, H.R. 1, that would require presidential and vice presidential candidates to disclose their tax returns.

But Trump was on everybody's mind.

Republicans immediately began sounding the alarm about congressional overreach if Democrats try to get the president's tax returns.

"Such an abuse of power would open a Pandora's Box. It would be tough to get the lid back on, it would set a very dangerous precedent," Pennsylvania Rep. Mike Kelly, the top Republican on the subcommittee, said in his opening statement. "Where does it end?"

"This would not be taking place if it were not about a duly-elected president by the name of Donald Trump sitting in that office. This is an incredible overreach," Kelly said.

Ways and Means Committee Chairman Richard Neal, D-Mass., is the only member of the chamber who can request the president's tax returns. He is expected to make the formal ask of the secretary of the Treasury Department, but has not laid out a timeline.

Republicans, one after the other, pointed out that it would be unprecedented for the Ways and Means Committee chairman to request the president’s tax returns.

Joseph Thorndike, the director of the Tax History Project, Tax Analysts said it was only unprecedented because all recent presidents before Trump had released their tax documents.

“There would be no need to request any president’s tax returns in the last 40 years because they’ve all been a matter of public record," Thorndike said.

Rep. Jackie Walorski, an Indiana Republican, used her questioning to illustrate that it was not required for presidential candidates to release their tax returns and there was no standard process for the candidates that did choose to.

"We're holding this hearing today under the guise of an academic discussion when in reality, this is all about weaponizing our tax laws to attack a political foe. Doing this I believe sets a dangerous precedent," Walorski said. "Privacy and civil liberties should still matter in this country."

Texas Republican Jodey Arrington said he was concerned about giving Congress the power to "abuse" the president and the voters who put him in office, even without seeing his tax returns.

“Did you see the election results? Because this was an issue during the presidential election,” Arrington asked a witness before answering his own question: “The American people were well aware of this and I’ve got a whole lot more confidence in the American people than they have in this body to conduct themselves in an objective and fair manner when it comes to these sorts of issues."

Rep. Tom Reed, the most moderate Republican on the panel, said he didn't deny that Neal had the authority to request Trump's tax returns, but urged the subcommittee to go another route that could get bipartisan support.

Neal is "a gentleman, I respect him, but I’m concerned about the next Ways and Means chairman," Reed said.

When Democrats took the microphone they were eager to paint the picture of a conflicted businessman who now occupied the White House and the need to look at his tax returns to better understand him.

“I just would appeal to my colleagues to not accuse us of lazy legislating to ask for these tax returns when we have such a conflicted president,” said Rep. Gwen Moore, Democrat of Wisconsin

They also used the expert witnesses to bolster their legal case if they decided to seek Trump's tax returns.

"We’re not interested in getting someone, we’re interested in following the law period. Give us the chance to do that," New Jersey Democratic Rep. Bill Pascrell said.

H.R. 1 is not expected to pass the Senate, and Democrats are expected to eventually request Trump's tax returns. But so far, they have taken a cautious approach that has rankled some progressives hoping for a more aggressive timeline.

Neal's spokeswoman said the chairman has not gone after Trump's tax returns right away because he is working to build a case for the likely chance that the case ends up going to court.

“Chairman Neal is building a case in the event that the administration decides to disregard federal law," said Erin Hatch, a spokeswoman for the committee.

Democrats have been quick to point out that Congress has a constitutional obligation of oversight of the executive branch.

“He was used to serving with a Republican Congress, House and Senate that was a rubber stamp to him. That won't be the case,” House Speaker Nancy Pelosi told USA TODAY in an exclusive interview just before she took power at the start of the year. “Oversight of government by the Congress is our responsibility."