More Republicans vowed to try to derail President Obama’s choice to head the Environmental Protection Agency Wednesday as Democrats rushed to her defense, touting her straight-shooting style and history of working for GOP governors, as well as industry leaders, when forging compromises.

Sen. John Hoeven, R-N.D., a key player in the Senate’s immigration reform push over the two weeks, took time out from those negotiations to talk about his views on Gina McCarthy’s chances of winning confirmation one day after Obama announced stricter new rules for power plant emissions in a major climate-change speech at Georgetown University.

“I think she had a tough route to confirmation before, and it’s tougher now,” he said in a brief interview.

Sen. John Boozman, R-Ark., who sits on the Senate Environment and Public Works Committee, said he plans to oppose McCarthy’s nomination over his frustration with what he called the EPA’s lack of transparency.

For years, Boozman said, the EPA has ignored repeated requests by Congress for scientific data supporting policies and rules established by the agency. During a confirmation hearing in April, he asked McCarthy whether she would change this practice if elevated to the top EPA post.

“You make these far-reaching decisions and you simply refuse to hand over the scientific data in which you make these decisions?” he said Wednesday. “We need openness, accountability – we simply never got that.”

Although McCarthy, who heads the EPA’s air and radiation office, responded during the hearing that she was “more than happy” to work with the senator to get him more information, Boozman said his complaints about the agency’s lack of openness are far broader and longstanding.

He specifically pointed to former EPA Administrator Lisa Jackson’s practice of conducting agency business on secret email accounts that shield officials from accountability.

Democrats supporting McCarthy’s nomination say Republican attempts to make her a scapegoat for the president’s new climate-change policies are completely misguided. McCarthy, who has served as an environmental adviser to five Massachusetts governors, including Mitt Romney, has spent 25 years working on environmental issues at the state and local levels and is known for her common-sense approach.

Moreover, if Republicans successfully sink her nomination, she will remain in charge of writing the very power-plant pollution rules they are trying to fight.

“The president has staked out a very clear position and whoever is the administrator is going to have to follow that policy – so it’s not like failing to confirm her is going to make climate change go away or make the president’s policy go away,” said Sen. Sheldon Whitehouse, a Democrat from Rhode Island who sits on the Environment and Public Works Committee.

“What refusing to confirm her does is take out a nominee who has worked for five GOP governors, has a lot of support and respect in the industry and who knows her way around the building and is famously good to work with,” he added.

McCarthy spent 25 years in public service in Massachusetts working for four different GOP governors, and before coming to Washington, served as the commissioner of Connecticut’s Department of Environmental Protection under Gov. Jodi Rell, a Republican.

Even before Obama’s climate change speech, some Republicans were planning to try to block her nomination. Sen. Roy Blunt, R-Mo., for instance, has a hold on her nomination over a parochial floodway issue that has been held up in his state for years.

Sen. David Vitter, a Republican from Louisiana and the ranking member of the environment panel, and other Republicans are taking issue with her personal integrity because she testified in April that the EPA was not working – at the time – on pursuing additional restrictions on power plant emissions, only to have the president contradict those statements with his new carbon limits this week.

Republicans opposed to her nomination say some Democrats share their concerns, although they declined to name which ones. So far, however, the likely Democratic suspects are remaining pretty mum.

Sen. Joe Manchin, a Democrat who represents coal-heavy West Virginia, on Tuesday issued a scathing statement reacting to Obama’s climate-change proposal, saying the restrictions would have “disastrous consequences” for the coal industry, as well as American jobs and the economy.

But Manchin’s office has yet to respond to two requests for comment on his view of McCarthy’s nomination.