Does a media-unit have an obligation to "turn over" a source that the President doesn't like? Is there a national security issue?

No, but the source has an obligation to sack up and allow the American people to see who is making these claims to provide context and assure them that this wasn't made up or some scheme dreamed up by a foreign power. I'm also not keen on the idea that someone on the inside would think they should act against the President. I don't care how much one despises any President, if they are making bad decisions, let them fail and allow the People to decide his fate. No one voted for this individual to act on their own to work in spite of a President's desired actions.

Personally, I think the NYT is either full of shit or someone has successfully conned them.

Hells naw. This situation wasn’t ‘National Security’ related. It was personal to him, and it wasn’t even ‘treasonous’.
The media has a right to protect sources the same as Trump, LE, the IC, and the military does. Get thicker skin.

Unfortunately the Writer does not have to give up their source which I don't agree with because on any article not just this one I could say an anonymous source and write whatever I want to.

My personal opinion is that what my parents have always told me. If you are going to do something or say something then OWN IT!!! Don't hide, don't deflect just own it. That is what I wish would happen...what is the worst thing that could happen in this case...Trump fires them. If you are going to work for someone loyalty goes a long way. Don't go behind my back.