Democratic chairman of Senate Intelligence Committee also urges a briefing, as president expresses 'surprise' at discovery of government records

Brain-damaging incidents, apparently as a result of directed-energy attacks, have also been reported in Florida

Counterintelligence chief also says officials do not believe anyone could manipulate voting results in meaningful way

National Counterintelligence and Security Center says Moscow and Beijing looking for ways to affect policy, while Tehran circulating disinformation, anti-American content online