If you have to deny that you’re bluffing, it’s pretty clear that you are bluffing.  Yet Vice President Joe Biden ran exactly that line in front of last week’s AIPAC conference.  America’s policy, he said,

is to prevent Iran from acquiring a nuclear weapon, period.  President Barack Obama is not bluffing.  He is not bluffing.

The next day, General James Mattis, Commander US Central Command, testified before the Senate Armed Services Committee, which included this exchange:

Senator James Inhofe (R, OK):  Are the current diplomatic and economic efforts to stop Iran from obtaining a nuclear weapons capability, are they working?
General Mattis: No sir…[Tehran’s] nuclear industry continues.

Indeed, the sanctions may well be hurting the Iranian people.  However, the Iranian government cares more about getting nuclear weapons than it does about the welfare of its people.  Since the sanctions aren’t hurting the government, they cannot work.

Informed by this mindset, the Iranian government is quite satisfied that the US is bluffing.  They’ve seen in all these years (not limited to the Obama years) no evidence that the US is serious on the matter of a nuclear armed Iran, no evidence that we will ever become serious, no evidence that we will go beyond sanctions to real moves to stop them.