It's based on logic. We know that those in the Obama administration have a bad reputation of using their office for political gain or to target their political advisories. Based on that, it makes sense that the holdovers still at the white house would continue with that trend by leaking information to make the president look bad in order to "RESIST". Given that the leaks serve no purpose other than making the president look bad, we know the ideology of whoever did it so it could be either a holdover from the Obama administration, or simply a leftist ideologue who was foolishly put in a position to handle sensitive information like that "Reality Winner" woman who was arrested earlier this year. Now that said, sure anything is possible, but those who don't have some kind of mental handicap (such as crippling political bias...which you are a good example of) should be able to figure out the type of people most likely to be behind the leaks.
