President Joe Biden is dropping his pick to fill the open seat on the Nuclear Regulatory Commission after a handful of Democrats joined Senate Republicans to block the nomination last year, HuffPost has learned.

Jeff Baran had held a seat on the five-person federal panel overseeing atomic energy and radiation safety since former President Barack Obama first named to the position in 2014. The Democratic commissioner easily won Senate approval when former President Donald Trump renominated him in 2018.

But pro-nuclear advocates angry over what they saw as Baran’s unwillingness to overhaul the regulatory process in favor of building new types of reactor technologies launched a campaign against the commissioner last year. With Republicans opposed to the nomination, the Biden administration needed almost every Democrat in the Senate to vote for Baran ― or leave the NRC without a tie-breaker for party-line votes between the four current commissioners.

The White House had wanted the Senate’s narrow Democratic majority to reconfirm Baran before his term ended last July. But as many as four senators on the Democratic side, including Sen. Joe Manchin (D-W.Va.) and Sen. Kyrsten Sinema (I-Ariz.), either planned to come out against Baran or refused to pledge their votes, according to a source with knowledge of the process. Neither senator’s office immediately responded to emails requesting comment on Monday.

When the Senate ended 2023 last month without a vote, the nomination automatically went back to the White House.

The NRC directed HuffPost’s questions about when the administration would name its nominee for the open commission seat to the White House, which did not respond to a request for comment.

But three sources with knowledge of the plans confirmed to HuffPost that the Biden administration does not plan to nominate Baran again. Two spoke to HuffPost on condition of anonymity because they were not authorized to comment publicly. The third claimed Baran’s loss as a victory.

“We killed this nomination,” said Ted Nordhaus, executive director of the Breakthrough Institute, a California-based climate think tank that advocates for more nuclear energy.

He was among the most vocal opponents of Baran’s nomination, and helped drum up votes against the Democratic commissioner. Nordhaus had cast Baran as a holdover from an earlier era of liberal regulators who saw their job primarily as safeguarding the public against the atomic energy industry.

“It is my job to focus on nuclear safety and security,” Baran said in 2017 at his reconfirmation hearing before the Senate Environment and Public Works committee. “It is not my job to weigh in on the pros and cons of the merits of nuclear power.”

That view, Nordhaus said, was common among Democrats for decades. But a modern outlook on nuclear safety has to consider not only the threats of using atomic energy, but the risks that not doing so increases pollution from fossil fuels that damages lungs and traps heat in the planet’s atmosphere, he said.

“Everyone went into this just assuming everybody would line up behind Baran, that this is just the kind of guy Democrats put on the commission,” Nordhaus said.

“The fact that enough Democratic senators were willing to say we’re not going to vote for this guy,” he added, “it’s pretty clear that for the first time in maybe ever a bunch of Democrats now recognize that we need reform at the NRC, that something has to change, that the technology can’t succeed if the NRC continues to approach this in the way it historically has.”

But Baran had defenders. The progressive pro-nuclear group Good Energy Collective previously told HuffPost Baran had a strong record of fighting for environmental justice and building relationships with communities saddled with radioactive pollution from the past.