Obama lied during his March 2015 TV interview when he said he learned about Hillary's private email system "the same time everybody else learned it, through news reports.

The New York Times reported on October 25, 2016:

[T]hat assertion concerned aides of Mrs. Clinton, who knew that the president himself had received emails from the private address, according to a hacked email made public on Tuesday by WikiLeaks.

"We need to clean this up – he has emails from her – they do not say state.gov," Cheryl D. Mills, a top aide, wrote to John D. Podesta, another senior adviser, on March 7, 2015.

We know Obama lied only because WikiLeaks released the hacked emails of John Podesta.  Podesta is not too popular with Obama and Hillary, given his penchant for telling the truth in his emails.  Unknowingly, Podesta is the Deep Throat of the Hillary Emailgate scandal.  We have to rely on WikiLeaks to inform use because the MSM have abandoned their duty of honest reporting to work for the election of Hillary.

Why did Obama lie?  He knew Hillary would be the Democratic nominee, and like it or not, he had to work to help elect her, as he has furiously done.  A Hillary win would keep his lies a secret since he never suspected that Podesta's emails would be hacked and released.  He did not want to be a party to and associated with Hillary's illegal use of a private non-secure email system.  It would damage his credibility and his legacy.  If Obama had told the truth, then Hillary could have used as a defense that Obama knew about the private email system and used it in his correspondence with Hillary, and therefore Obama implicitly approved of Hillary's private email system.  Obama tacitly approved of Hillary's email system because he knew and did not order her to stop.  Hillary knew that Obama had lied, so she must have felt safe.

We know that Obama and Hillary lied when they said the cause of the 2012 Benghazi attack was a video.  We know that Obama lied when he said Obamacare would lower health insurance premiums by at least 25%, when in fact the rates have doubled and tripled, and will continue to rise from 30% to over 100%.

In summary, Obama has lied to us on three major issues: the cost of Obamacare, the cause of Benghazi, and his knowledge of Hillary's illegal private email system.  Hillary participated in the lies about Benghazi and when Obama learned about her email system.