The House Committee on Science, Space and Technology held a hearing Wednesday seemingly with the goal of affirming that chairman Lamar Smith (R-Texas) has the authority to subpoena those investigating whether the oil industry covered up what it knew about climate change.

But Democrats on the committee used the hearing to slam Smith and the GOP for what they say are embarrassing efforts to defend the oil industry.

Before a lengthy back-and-forth in which many, including three expert legal witnesses, came to Smith’s defense, ranking committee member Eddie Bernice Johnson (D-Texas) blasted the longtime climate change denier, calling his actions embarrassing, ironic and a brazen attempt to help ExxonMobil.

Since being established 58 years ago, Johnson said, the House committee has effectively and appropriately used its oversight authority. That’s no longer true, she said, because of Smith.

“Today the majority [party] seems to view its oversight powers as a political tool, and the committee’s investigative authority as unbounded,” Johnson said. “This hearing appears to be the culmination of a politically motivated ‘oversight’ agenda that has been applauded by oil, gas and mining interests and broadly condemned by the public, the media and the independent scientific community across the country and around the world.”

House Committee on Science Space and Technology/YouTube Rep. Eddie Bernice Johnson (D-Texas) speaks during Wednesday's hearing of the House Committee on Science, Space and Technology.

In July, Smith subpoenaed the New York and Massachusetts attorneys general, along with several environmental groups who are investigating whether companies like Exxon Mobil committed fraud by covering up the risks of carbon emissions and climate change. At the time, Smith questioned the investigating groups’ motives, saying they want “companies to settle out of court so they can obtain funds for their own purposes.”

Smith and other Republicans maintain that the probes threaten free speech rights ― an argument that has been a go-to defense for the industry.

The irony, Johnson said, is that in issuing subpoenas aimed at protecting Exxon’s free speech rights, Smith is “unequivocally violating these [subpoenaed] groups’ First Amendment rights to petition the government.”

The offices of New York Attorney General Eric Schneiderman and Massachusetts Attorney General Maura Healy have refused to comply with Smith’s demands, calling them “unconstitutional,” “unprecedented” and “dangerous.”

During Wednesday’s hearing, Smith said the documents he’s demanding in the subpoenas would inform the committee as to whether the investigations are having a “chilling impact on scientific research and development.” He said the AGs and environmental groups could face “consequences,” including depositions, contempt proceedings and legal action, if they do not turn over the information.

“The committee wants the truth, Americans deserve the truth and the constitution requires that we seek the truth,” said Smith, who has received $684,947 in donations from the oil and gas industry since 1989. “The refusal of the attorneys general to comply with the committee’s subpoenas should trouble everyone sitting on this dais, everyone in this room, and every American.”

Although many Republicans agree, Democratic members of the committee did not mince words Wednesday when describing their disgust with Smith.

Bill Clark via Getty Images Rep. Lamar Smith (R-Texas) has a long history of denying climate change.

Johnson fired off an extensive list of times she says Smith has “abused” the committee’s oversight powers, including harassing NOAA climate scientists in an “attempt to undercut the notion of human-caused climate change.”

The “latest embarrassment of the committee,” Johnson said, is Smith and the majority party’s “brazen attempts to assist ExxonMobil in the face of legitimate fraud investigations.”

“The majority has claimed that their investigation is about protecting the First Amendment rights of ExxonMobil,” Johnson said. “However, the law is clear ― fraud is not protected by the First Amendment. If any companies in the oil industry defrauded the public or their shareholders in their well-documented disinformation campaign on global warming, then that is a matter for the state attorneys general and the courts, not the Committee on Science.”

Rep. Paul Tonko (D-N.Y.) said he is concerned the subpoenas might interfere with legitimate investigations of fraud, set a bad precedent and damage the committee’s credibility.

“There is an obvious political agenda here, I believe, and I hope that we will put an end to infringing on states’ rights so that our AGs can conduct their rightful enforcement of the law,” Tonko said.

Of the four expert witnesses called for Wednesday’s hearing, three agreed the committee has the authority to issue subpoenas.

One of those three, Jonathan Turley of George Washington University Law School, said that even though he agrees with the science behind climate change, the actions by state AGs “contravenes academic freedom and free speech.”

The fourth expert witness, Charles Tiefer, of the University of Baltimore, warned that “no House committee has ever tried, or should ever try” to enforce a subpoena against state attorneys general.

“Today, a House committee with no precedent is going squarely against a key component of state sovereignty,” Tiefer said.

Just before Wednesday’s hearing, the #ExxonKnew campaign hosted a press conference on Capitol Hill in which a number of speakers blasted the committee’s ongoing efforts to interfere with their investigations.

“This hearing may as well be sponsored by ExxonMobil,” May Boeve, executive director of 350.org, one of the subpoenaed groups, said in a statement. “The bottom line is that this hearing is nothing but Smith’s attempt to distract us from the real issue: Exxon knew the truth about climate change, and Exxon lied.”

Watch Wednesday’s hearing in its entirety below.

This article initially identified Rep. Paul Tonko by his middle name, David, and has been updated.