An engineer at a nuclear power plant has been charged with sending threatening letters containing a powdery substance to a country club where President Bush is scheduled to appear Tuesday for a Republican campaign event.

Michael Lee Braun, 51, was arraigned Monday in U.S. District Court in Sacramento on two federal charges of sending threats through the mail. Each carries a maximum penalty of 5 years in prison and a $250,000 fine.

The charges are connected to two letters prosecutors said Braun mailed on Thursday to the Serrano Country Club and Serrano Visitors Center in El Dorado Hills, a tony community in the foothills east of Sacramento. Bush plans to appear at the club Tuesday afternoon in a campaign event for U.S. Rep. John Doolittle, R-Calif.

The letters contained threats to President Bush, Vice President Dick Cheney and Doolittle, according to an FBI statement.

A federal affidavit said that Braun has sent 51 threatening letters, including the two most recent ones, since the 2001 terrorist attacks. The letters threatened the lives of the president, Cheney, First Lady Laura Bush and Defense Secretary Donald Rumsfeld.

"Each of the letters contained a written threat, usually death by some kind of WMD agent (anthrax, toxic chemical poison, radioactive dust or improvised explosives) and some unknown, white, powdery substance, or items simulating a possible letter/package improvised explosive device," the affidavit said.

The white substance usually turned out to be baking soda, the affidavit said.

Braun's attorney, Philip Cozens, declined to comment Monday, saying he had just taken the case.

FBI spokeswoman Karen Ernst said the case was "not believed to be related" to the ongoing probe into the anthrax used in mailings that killed five people in 2001.

Braun was arrested Friday. Federal officials also served search warrants at his home in Elk Grove, a suburb south of Sacramento, and at the decommissioned Rancho Seco nuclear power plant, which is owned by the Sacramento Municipal Utility District.

The affidavit said Braun has a master's degree in radiological physics and a law degree. He has worked as a nuclear engineer at Rancho Seco since 1984 while practicing law part-time.