The Senate Intelligence Committee has sent formal requests to more than a dozen organizations, agencies and individuals, asking them to preserve all materials related to the committee’s investigation into Russian interference in the 2016 election and related issues, according to a congressional aide. The committee chairman, Sen. Richard Burr, R-N.C., and its vice chairman, Sen. Mark Warner, D-Va., sent letters Friday, the same day committee members received a classified briefing from FBI Director James Comey.