Nowruz greetings == good, Netanyahu's speech == bad

Why is it all right for the President of the United States to send a video letter to the Iranian people filled with smarmy Nowruz greetings and lobbying the Iranian people to support Obama's nuke deal with Iran, but it is not all right for the Prime Minister of Israel, the country that would be most threatened by Iranian nuclear weapons, to deliver a speech before the American Congress lobbying against the deal?