How is this legal? Also, given the difficulty some Trump appointees (Kushner) have had with getting clearances, this is of the utmost hypocrisy or clearances and security classification means very little.

It’s not. But who will stop it?

Citation needed. The President has complete, unilateral classification and declassification authority. He can also grant or withdraw clearance to/from anyone, without any background checks.

Ah. So this is either the absolute height of hypocrisy, or the whole clearance and classification system was and is meaningless, just rigamarole. Here's some red tape to get rid of, easy.

Winning an US presidential election is the polar opposite of "easy".