I believe campaign donations over $8000 must be disclosed, and the claim is that they were not. In the US, much smaller donations must be disclosed. As far as gifts, I think Congressmen cannot accept more than $50. Mostly, much of what Netanyahu received was "gifts", such as free travel on an airplane. Incidentally, When Obama's wife or kids travel along with him, they must pay their own way.
Trump: Middle East would be more stable if Saddam, Gaddafi still in power (Reuters)
from the article: State Comptroller: Public officials cannot accept private travel funds