Chuck Schumer responded that he is happy to talk about this contact with Putin. They met publicly in 2003, and Schumer didn't say otherwise while under oath.
Three hours, and three attempts at spelling "hereby" later, Trump sent another shot:
Is he really calling for an investigation?
The case against: Trump was being ironic. He was painting the talk about his ties with Russia as hyperventilation and used the opportunity to rib the Democrats.
The case for: Trump is the president of the United States. His words carry meaning, and the public must be able to assume that the words he uses represent what he means.
Why it matters: Trump is the first president to use Twitter as the primary means of delivering statements. His words move markets and affect policy decisions worldwide. The public has to know what Trump means when he speaks, and misunderstood messages could do damage.