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Mr. Magwood disputed a claim by Senate Majority Leader Harry Reid, Nevada Democrat, that the allegations against Mr. Jaczko were politically motivated. Mr. Jaczko worked for Mr.  Reid before joining the NRC, and Mr. Reid’s strong support for Mr. Jaczko is considered crucial in keeping his job.

Mr. Reid is the leading congressional opponent of a planned nuclear waste dump at Yucca Mountain in Nevada. Mr. Jaczko has made a series of decisions over the past two years that have aided the Obama administration’s goal of shutting down Yucca Mountain.

Mr. Jaczko apologized for the distraction that had been created during his 2½ years in the job and said he looked forward to discussing ways “to improve communication and trust.” He said he had no plans to step down.

Mr. Ostendorff said the issue was not Yucca Mountain or party politics, but Mr. Jaczko’s “bullying and intimidation” of NRC staffers and even some commissioners, which Mr. Ostendorff said “should not and cannot be tolerated.”

Mr. Ostendorff said he had “lost faith” in Mr. Jaczko’s ability to lead the commission.

White House Chief of Staff Bill Daley said this week that problems at the NRC stem from the commission’s “strong chairman” structure, in which the leader of the five-member panel has far greater powers than the remaining four commissioners.