Congress is wading deeper into what could become a major new feud over climate change.

The climate fight began earlier this year when 17 Democratic state attorneys general, led by the U.S. Virgin Islands and New York, began issuing subpoenas to oil giant Exxon Mobil over whether it covered up research its scientists found on climate change, which the company adamantly denies.

The fight spurred lawmakers in Washington to get in on the action. The Republicans argue against the investigations as an affront to free speech and the Constitution.

The Democrats, on the other side, are defending the attorneys general, while urging the Justice Department and Attorney General Loretta Lynch to ignore GOP critics and pursue its own investigation.

Lynch told the Senate Judiciary Committee in March that she was looking into the possibility of prosecuting "climate change deniers." Lynch also asked the FBI "to consider whether or not it meets the criteria for which we could take action."

The attorneys general were spurred by news reports that Exxon had known for decades about the risks posed by climate change, but chose not to disclose the data found by its scientists. The attorneys general argue that constitutes fraud. Many scientists blame the burning of fossil fuels such as crude oil for driving manmade climate change.

Congressional Republicans began pushing back against the state investigations by sending letters to the attorneys general last month, prodding them for all emails and communications between the AGs and environmental groups. They also sent letters to environmental groups prodding them for correspondence.

Political strategists say the GOP wants to show the attack on Exxon was a collaboration between climate activists and the states to push a political agenda, rather than a real attempt to find wrongdoing.

The GOP letter, signed by a coalition of House science committee lawmakers and Chairman Lamar Smith of Texas, calls out the Exxon investigation as baseless.

"The committee is concerned that these efforts to silence speech are based on political theater rather than legal or scientific arguments, and that they run counter to an attorney general's duty to serve 'as the guardian of the legal rights of the citizens,'" the letter reads.

California Democrats responded to the letter, calling the GOP's pressure campaign an abuse of power.

"Chairman Lamar Smith is abusing his power and wrongfully accusing" the attorneys general of violating the First Amendment, said Rep. Ted Lieu in a statement after sending a letter of support to his state's attorney general, Kamala Harris, who is part of the group investigating Exxon Mobil. "We support her investigation."

Meanwhile, Senate Democrats were busy urging Lynch to ignore Republican attempts to keep the federal government from getting involved. After Lynch spoke to the Judiciary Committee earlier in the year, the Senate GOP sent her a letter not to proceed.

Presidential candidate Sen. Bernie Sanders, D-Vt., sent a letter of support to her in May, with liberal Sens. Elizabeth Warren of Massachusetts and Sheldon Whitehouse of Rhode Island, blasting Republicans for attempting to stop any investigation.

The Democrats say the GOP's argument "reprises the tobacco lawsuit's own early history of efforts from Congress to discourage or interfere with that lawsuit in order to protect the tobacco industry," the letter reads.

A legal settlement between tobacco companies and more than 40 attorneys general in the 1990s is regularly referred to by those supporting legal action against climate deniers. The states used antitrust and consumer protection laws to get the companies to agree to pay the states annually for the damage to public health caused by cigarette smoking, among other penalties.

The latest Republican letter to Lynch about the investigation was sent June 13 by Rep. John Radcliffe, R-Texas, chairman of the infrastructure and cybersecurity panel of the homeland security committee, and four other lawmakers.

The letter asks her to resist getting involved in a state-led investigation that is meant only to silence political rivals.

"In America, we do not prosecute our political opponents, much less those who merely express views on policy that differ from our own," the letter reads. "It is not the role of law enforcement officials [the AGs] to address perceived shortcomings in our legislative process by using their investigative and prosecutorial powers to bully private entities into compliance with their preferred policies."

Exxon on June 15 filed a retaliatory strike at the attorneys general by asking a federal court in Texas to block the investigation started by Massachusetts AG Maura Healey.

"The great irony here is that we've acknowledged the risks of climate change for more than a decade, have supported a carbon tax as the better policy option and spent more than $7 billion on research and technologies to reduce emissions," said Exxon Mobil spokesman Allan Jeffers. "It should make people question what this is really all about."

Lawyers and strategists say the state investigations are more "grandstanding" than anything else, especially after the Supreme Court halted the Obama administration's climate rules in February. Many of the states pursuing the investigations support the president's climate agenda and have vowed to continue to push for a climate policy despite the high court's stay.

"The people following Exxon are trying to follow the precedent of tobacco litigation," said Brendan Collins, partner with the law firm Ballard Spahr and an expert on environmental regulations. He said "the reality is a very different situation" when comparing what Exxon is accused of doing and the arguments laid out in the tobacco suits.

The evidence brought against the tobacco industry two decades ago is "pretty substantially different from the idea that Exxon may have duped me from getting a low-mileage [car] and now the island of Tuvalu is going to get covered by water," Collins said.

It's a "very big leap" to link what Exxon "did or didn't do" to the harm posed by climate change.

The cracks in the argument against the oil company are beginning to show.

The Virgin Islands attorney general, Claude Walker, grabbed headlines when he subpoenaed the conservative-leaning group Competitive Enterprise Institute, which had a working relationship with the oil company and is known as a global warming skeptic.

The attorney general later withdrew the subpoena after the think tank pushed back in D.C. Superior Court last month with a motion to sanction him, claiming a violation of First Amendment rights.

Think tank President Kent Lassman in a call with reporters last week called the AGs' attack a "massive fishing expedition" meant "to shut down the debate on global warming on the basis of their so-called law enforcement powers."

He agreed with Collins that the tobacco argument is a bridge too far. "That involved the sale of tobacco, this involves a policy debate," Lassman said. "They might think they have precedent in the tobacco [litigation]. They do not."

In the end, it might result in just a "public relations black eye for Exxon," and nothing more, Collins said.

The type of letter-writing campaign seen in recent weeks likely will continue on Capitol Hill, but nothing more substantive like a hearing, observers said.

"If you do a hearing, what are you going to get out of it?" a Republican strategist asked. "In some way it's a lot of noise, but nothing happens."