"I don't see a difference between denouncing and rejecting" - Barack Obama
Barack Obama was being totally honest. He doesn't...
Here's the difference. Courtesy of Merriam.
Denounce - to pronounce especially publicly to be blameworthy or evil
Reject - to refuse to accept, consider, submit to, take for some purpose, or use
If you were President, it could be the difference between just condemning the actions of a nation or moving aggressively and cutting off trade or diplomatic ties with that nation.
And that is a considerable difference.
But it's only words... so who cares?!