Secretary Jim Mattis responds to Putin's call for increased intelligence cooperation with U.S., NATO
Leaking, the president says in a tweet, "has been a big problem in Washington for years"
Vessel sailing near U.S. sub base in Connecticut has sophisticated surveillance equipment that can intercept radar and other electronic signals
New U.S. secretary of state will meet with Russian's top diplomat and those of other nations in Germany this week
Peter Wehner says if collusion with Russia is proven, it could sink Trump's presidency