Former US Secretary of State Alexander Haig, 85, is critically ill in hospital, a spokesman says.
He was admitted on 28 January, but Johns Hopkins Hospital in Baltimore did not specify his illness.
He was presidential adviser to President Richard Nixon during the Watergate scandal in the early 1970s.
President Ronald Reagan appointed him secretary of state. He famously said "I'm in charge here" after the attempted assassination of Mr Reagan.
In fact, several other officials were ahead of him in the hierarchy.
Mr Haig had ambitions for the highest office but few people took him seriously from then on as a presidential candidate.
The four-star general and Nato supreme allied commander ran for president in 1988.
Under President Nixon he was appointed White House chief of staff in 1973. He helped the president prepare his impeachment defence in July 1974.