Rub your eyes. One minute Iran is a principal enemy of civilization – sponsoring terror around the world, arming the Assad regime’s mass slaughter in Syria, developing nuclear weapons to further its war against the West and its declared aim of exterminating Israel. The next minute it has become America’s ally and the West’s new best friend.The US says it is “open to engaging the Iranians” over the crisis in Iraq. The reason for the volte-face is that the Islamic State in Iraq and Syria (ISIS), a savage terrorist army previously known as al-Qaida in Iraq, has routed the Iraqi army and now controls territory from the outskirts of Aleppo in Syria to Fallujah and Mosul in Iraq, even threatening Baghdad.The prospect of such a well-equipped and financed fanatical force controlling a swathe of Iraq is an unconscionable threat to the West. It puts oil supplies in jeopardy, creates an enormous territorial infrastructure for holy war and will serve as Indoctrination Central for even more Muslim youths pouring in from the UK and Europe to be trained and sent back to their host countries to perpetrate terrorist atrocities.Notwithstanding this catastrophe, the US has no intention of getting sucked back into Iraq. Enter Iran, which has offered its ally, Iraq’s Shia Prime Minister Nouri al-Maliki, the use of its army, its spies and its fearsome Revolutionary Guards to deal with the ISIS Sunni insurgency.There are many Western voices saying that, despite Iran’s record, the West should ally with it in dealing with their common enemy in ISIS and stabilizing Iraq. But any cozying up to Iran would be astonishingly short-sighted. For sometimes my enemy’s enemy is also my enemy. And Iran remains the West’s deadly enemy.Since the 1979 Islamic Revolution, Iran has been in a state of self-declared war against the West. The State Department considers it to be the world’s leading state sponsor of terrorism. It supports Hamas and Hezbollah, and has been behind countless murderous attacks against US, Jewish and other Western interests.The idea that Iran has an interest in stabilizing Iraq is the opposite of the truth. Iran has every interest in destabilizing Iraq. Since the fall of Saddam, it has been doing precisely that.After years of supporting Shia militias fomenting sectarian strife in Iraq and blowing up US and coalition soldiers there with its roadside bombs, Iran signed a deal last February to sell Iraq arms and ammunition worth $195 million, in violation of international arms trade laws. The aim was to continue to support the Shia militias in terrorist violence against the Sunni minority.If Iran now embeds itself in Iraq, the country will be permanently destabilized.Saudi-backed Sunni militias will fight back, with the risk of dividing Iraq into two armed camps, Shia and Sunni.These would not only fight each other, but would create two separate Iraqi terrorist bases for jihadi attacks against the West.At the same time, if the West allies with Iran it will also be helping keep its murderous puppet Assad in power in Syria.And if the US really is desperate to use Iran as its proxy against ISIS, that will undermine what remains of the West’s bargaining power in the negotiations to destroy Iran’s capacity to make nuclear weapons.Such an unholy alliance could therefore end up handing Iran a double victory on a plate. Indeed, it’s almost as if it is behind the whole thing.Although this must be purely speculative, it is not entirely fanciful. For in the Arab and Muslim world, forces can simultaneously be allies and enemies.Although ISIS is a Sunni force and is supposedly at war with the Assad regime in Syria, there is evidence to suggest that both Iran and its Syrian puppet regime may have cooperated with it. In 2012, the US Treasury Department identified Iran as supporting the ISIS precursor, al-Qaida in Iraq. And ISIS is thought to have done oil deals with the Assad regime itself, which some analysts speculate may have wanted to boost jihadi fighters in order to discredit the opposition in Western eyes.It is possible, therefore, that having used ISIS for its own devious ends Iran now finds its activities have got out of hand. Even if Iran had nothing to do with ISIS, however, any Western overtures to the clerical regime would be a serious error.This week, the Iranian leadership suggested the price of its “help” in “stabilizing” Iraq would be a deal over its nuclear program. State Department denials that these two issues would be in any way linked lack a certain credibility. This is because, since the start of the Geneva negotiations, it has appeared that the US and the rest are determined to do a deal with Iran, even if this is a rotten deal that won’t prevent it from reaching nuclear breakout capacity.Indeed, it is not too cynical to suspect that the Obama administration may be eyeing the Iraq crisis as potential diplomatic cover for a nuclear sell-out to Iran for which it always intended to settle.Moreover, by his own admission Obama aims to achieve a strategic realignment in which Iran is transformed from the enemy of the West into its ally, stabilizing the region by creating a supposed equilibrium of power against Iran’s Sunni enemy, Saudi Arabia.This is a strategic error of the first magnitude.To give Iran the edge will not produce regional stability. The more Iran is empowered, the more Saudi Arabia will fight it. The outcome will be a hugely increased likelihood of war and endemic tribal conflict engulfing the region.In addition, both Iran and Saudi are working not just against each other but to destroy and dominate the West. As such, both should be seen as the West’s mortal enemies. The Western aim, therefore, should be to defeat or at very least box in both of them.Iraq has turned into a catastrophe because, when the US pulled out, the Obama administration left a vacuum in which Maliki pumped up tribal conflict and paved the way for the ISIS insurgency.Iran, the most manipulative and sophisticated geopolitical strategic player in the world, understands that Obama’s desperation to turn his back on the threats from the Islamic world has left the US weakened and exposed. Whatever its origins, the Iraq crisis offers Iran an opportunity to exploit that weakness, a threat with which the West now seems too paralyzed to deal.Melanie Phillips is a columnist for The Times (UK).