It is clear that James Clapper knowingly and definitively lied while under oath.
On March 12th, Oregon Senator Ron Wyden questioned James Clapper in a Senate Intelligence Committee Hearing. When asked, "Does the NSA collect any type of data at all on millions or hundreds of millions of Americans?” James Clapper sunk his head into his hand and responded, "No sir... Not wittingly." He later clarified that (in his opinion) this was the "most truthful or least untruthful manner" of answering the question (which by the way was sent to Director Clapper's office a day earlier to ensure time to formulate a clear and accurate answer).
Both the question and answer to the American people were very clear. Due to his deliberate lie under oath, James Clapper should be charged and tried for perjury.