I am guessing the Iranians believe Obama won't aid Israel if they get into a shooting war with Iran. In fact I bet Iran is betting on Obama actively opposing Israel with harsh Sanctions if such comes about.
Yes, Obama's projection of American weakness around the world emboldens despotic belligerent regimes like Iran. Quite a contrast with how the Iranians released the American hostages just as Reagan was inaugurated. They were fearful of the US then, but not now.