Republicans on the House Committee on Foreign Affairs attempted to derail a hearing on the U.S. role in global climate action with a ferocious attack on Presidential Special Envoy for Climate John Kerry, following allegations that he had shared sensitive information with Iran’s foreign minister.

With a masked Kerry speaking before the committee, the Wednesday hearing signaled a determined GOP effort to undermine his credibility and, with it, President Joe Biden’s efforts to re-establish U.S. leadership on climate at home and abroad.

When not facing questions about his past communications with Iranian Foreign Minister Mohammad Javad Zarif, the former secretary of state was confronted with tough questions from both sides of the aisle about China’s ongoing construction of new coal plants and its persecution of its Uyghur Muslim minority.

While clearly unprepared for the grilling on Zarif, Kerry was mostly able to stay on message on the Biden administration’s commitment to the goals of the Paris climate accord — holding global warming to 1.5 degrees Celsius — and the economic opportunities and jobs the clean energy transition will generate.

“Just as America led the world in the Industrial Revolution, just as we lead the technological revolution, we can and will lead the energy revolution,” he said in his opening statement. “We can and will develop the battery storage technologies, direct air capture technologies, the green hydrogen, the smart grid technologies that will change the world and stave off the catastrophic impacts of the climate crisis,” he said.

He also underlined the movement of global capital toward clean investments, pointing to initiatives like the Net Zero Asset Managers group of 87 global investment firms that have committed to moving assets toward the low-carbon resources that will be needed to get to net zero by 2050. Influential U.S. firms Blackrock, Vanguard and State Street Global Advisors have all signed on.

The Zarif allegations first surfaced in an April 25 article in the New York Times, which included a single remark Zarif made in a leaked tape about Kerry telling him about Israeli air strikes on Syria. Kerry quickly and categorically denied Zarif’s statement, as he did again during the hearing, but some Republicans continued to make it a flashpoint.

Not content with quizzing Kerry about the Zarif allegations, Rep. Scott Perry (R-Pa.) asked him about an official fact-finding trip he made to Nicaragua in 1986, when he was a senator, and a 2006 trip to Syria. Rep. Lee Zeldin (R-NY) asked for details about a conversation between Kerry and Zarif that, he said, he had seen during a conference in Munich in 2019. Rep. Ann Wagner (R-Mo.) held up a copy of a letter she had sent to Secretary of State Antony Blinken asking for a formal investigation of Kerry’s relationship with Zarif.

Rep. Dean Phillips (D-Minn.) was the sole Democrat to come to Kerry’s defense. Identifying himself as a “Gold Star son” who lost his father in the Vietnam war, Phillips said, “I am saddened that some of my colleagues would seemingly put [their] faith in the word of the Iranian foreign minister over that of yours. I’m sorry for that. The irony is not lost on me.”

‘Don’t Trust, Verify’

Beyond the Zarif allegations, one of the key takeaways from the hearing was that China will be a major bargaining chip in congressional negotiations over Biden’s ambitious plans to decarbonize the U.S. economy.

China now produces about 27% of the world’s carbon emissions, versus the 11% now generated in the U.S. While standing up large amounts of renewables, China continues to build new coal plants not only at home but in developing nations around the world. President Xi Jinping has committed China to peaking its carbon emissions by 2030 and reaching net zero by 2060.

But both Democrats and Republicans questioned whether the Chinese could be trusted to meet even those commitments. They also expressed concern about reports that Uyghurs are being used as forced labor at factories producing clothing and high-tech goods for the U.S. market.

Rep. Brad Sherman (D-Calif.) said that while Xi may now be using the words “climate crisis” in public statements, he “may not actually do anything on the ground. Every week they build a new, large coal-fired plant, week after week.

“You’re a very good diplomat, very persuasive,” he said to Kerry. “But all you have in your toolbox is a chance to appeal to the conscience of a regime that puts its own people by the millions in concentration camps.”

Noting that China dominates the supply chain for solar panels and critical minerals, Rep. Michael McCaul (R-Tex.), the committee’s ranking member, said that in any negotiations with the country, climate and human rights concerns should be intertwined.

“How can you assure us that [in] this quest we’re on [to reduce emissions], that slave labor and Uyghur genocide taking place as we speak are never part of the climate solution in the United States?” he said.

McCaul is one of three Republican representatives who have introduced the Paris Transparency and Accountability Act, which he said calls for the renegotiation of the Paris agreement “to create a level playing field. And it calls for the new agreement to be submitted for Senate approval [to] ensure there is sufficient oversight of the commitments the president makes on behalf of the American people.”

The bill also would require any renegotiated agreement to include information on how both China and Russia will meet their climate commitments and on how the U.S. would “counter malign Chinese, Russian and other adversarial influence and domination over energy supply chains.”

Kerry acknowledged the difficulties of negotiating with China, especially on human rights issues. “It’s a different attitude about what they are willing to acknowledge or not acknowledge,” he said. “So, a decision has to be made by Congress or the administration [on] how we will respond to that.”

One possibility under discussion, he said, is a “border adjustment mechanism. This is a mechanism which President Biden has asked us to evaluate as a means of placing an additional cost on goods that come from places that are not responsible in what they are doing or how they are being produced.”

But, he said, the broader economic and human rights issues are “not my lane. My lane is very specifically to try to get the Chinese to move to do what we need to do with respect to climate itself.”

Kerry’s motto, he said, is “don’t trust, but verify. In this endeavor with China, you’ve got to be eyes wide open.”