Ten Republican state attorneys general sent a letter to President Trump Wednesday spelling out the legal reasons why he should back out of the Paris climate deal or risk eroding key pieces of his energy agenda.

First, withdrawing from the Paris climate change agreement "is an important and necessary step toward reversing the harmful energy policies and unlawful overreach of the Obama era," read the letter led by Attorney General Patrick Morrisey of West Virginia. The attorneys general of Alabama, Arkansas, Kansas, Louisiana, Missouri, Nebraska, South Carolina, Texas and Wisconsin also signed the letter.

The letter is the latest message relayed directly to the president on why he must leave the Paris climate agreement, as opposed to the many messages Trump is receiving from those wanting the U.S. to remain a party to the deal. On Wednesday, Pope Francis gave Trump a signed copy of his 2015 encyclical on climate change while urging him not to leave the agreement.

Secretary of State Rex Tillerson later said that the president has not made a decision on the Paris deal after Trump and Tillerson met with Vatican and Italian government officials to discuss the subject Wednesday.

"The president indicated we're still thinking about that, that he hasn't made a final decision," Tillerson said. A decision will be made "when we return from this trip," Tillerson told reporters. Tillerson has supported remaining a party to the agreement.

Trump will be returning home after the May 26-28 meeting of the Group of Seven industrialized nations in Sicily. He is expected to hear more from G7 leaders and diplomats who urge him not to pull out of the agreement.

Wednesday's letter from Morrisey and the other attorneys general is the exact opposite of what he can expect to hear from the G7.

Outside of vanquishing the energy and climate policies of the Obama administration, the Republican attorneys general say there are pressing legal reasons for exiting the deal even though it is technically nonbinding.

"Let us be clear at the outset: We do not believe the Paris Agreement legally binds the United States to take any action," the letter read. "As even the prior administration acknowledged, the Paris Agreement is at most 'politically binding.'" However, the agreement's nonbinding nature "does not mean there are no consequences to remaining in or withdrawing from the agreement."

The 10 state attorneys general explained that as long as the U.S. remains a party to the agreement, "there is a risk that some individual or organization will attempt to enforce its terms," the letter read. They believe the legal grounds exist for a lawsuit because the deal does not allow any nation to downgrade its commitment to cut emissions. Under the deal, a nation is allowed only to increase its commitments.

"While we do not believe that such an enforcement lawsuit should prevail, we cannot be sure that the judge who might decide such a claim would necessarily rule that way," the letter stated.

"Second, participation in the agreement could be used to challenge your administration's welcome efforts to revise or rescind regulations promulgated by President Obama, including the so-called 'Clean Power Plan,'" the letter read.

"For example, the United States' reduction of carbon emissions under the Paris Agreement is premised on the Clean Power Plan going into effect. Advocates of the Clean Power Plan could argue that the United States' continued commitment to the Paris Agreement makes any effort to revise or rescind the Clean Power Plan arbitrary and capricious," they said. "Again, while we do not believe this argument has any merit, it is nevertheless an unnecessary risk of remaining in the Paris Agreement."

Third, a number of environmental law scholars argue that the U.S.'s continued involvement in the Paris Agreement "triggers" a section of the Clean Air Act that the Environmental Protection Agency can use "to force states to reduce carbon dioxide emissions."

Meanwhile, the conservative group American Energy Alliance created a website, StopParisAgreement.org, to urge citizens to sign a petition for the U.S. to exit the deal.

Tom Pyle, the president of the group, is the former head of President Trump's Energy Department transition team.

"Remaining in the Paris Climate Agreement would be an ‘America last' approach — quite the opposite of what Donald Trump promised during his bid for the presidency," Pyle said. "We urge President Trump to protect American families and businesses from unnecessary and burdensome climate regulations by withdrawing from the Paris deal."