Mitt Romney, the Republican candidate in the US presidential election, has indicated that he will adopt a tougher position towards Russia than his rival, the incumbent president, Barack Obama. Rivalry with Russia is unlikely to dominate Mr Romney's foreign policy, because Russia has neither the agenda nor the heft of the Soviet Union.

Yet in important areas-nuclear arms control, missile defence and crises in the Middle East-a Romney presidency could result in markedly higher levels of tension with Russia. This could narrow the scope for co-operation generally, and encourage Russia to develop partnerships in Asia.

In March Mr Romney criticised Mr Obama for being too soft on Russia, which he described as the US's "greatest geopolitical foe". It is easy to dismiss the comment as campaign hyperbole, especially as it was made by a politician who has been a pragmatist in the past, and because the position of Russia in the world is different from that of the Soviet Union. Nevertheless, US-Russian relations are still important, as is the question of what impact a Romney presidency would have.

The cold war between the US and the Soviet Union was the defining geopolitical relationship of the second half of the 20th century, and Europe was the principal region in which their struggle was waged. In the 21st century the defining geopolitical relationship is likely to be US-China and the main arena of competition the Asia-Pacific region. Russia's global weight has correspondingly shrunk. Russia still matters in US foreign policy, because of its permanent seat on the UN Security Council, its ties to states such as Iran and Syria, its influence on Europe, and its possession of the world's second-largest arsenal of nuclear weapons.

Mind the missile gap

In the nuclear weapons sphere, a Romney presidency has the greatest potential to change the course of US-Russia relations. Mr Obama aspires to a nuclear-free world through phased cuts in the arsenals of the nuclear powers, and in the first instance this concerns the US and Russia. To achieve this, he has indicated that he can show some flexibility with regard to US plans for ballistic missile defences deployed in Europe and elsewhere. Mr Romney's advisers see things differently: they have no wish to accept limitations on US development of missile-defence capabilities, and show little interest in new arms-control agreements.

A Romney presidency could therefore cause a breakdown over issues that Mr Obama might be able to finesse. Mr Obama's scope for concessions on missile defence might be limited, but he could meet Russian concerns in related areas such as the deployment of US tactical nuclear weapons in Europe, or engage in other confidence-building measures. Because Mr Romney's advisers do not seek nuclear disarmament, there seems little reason for them to compromise on missile defence or to advocate measures designed to assuage Russian concerns.

Circumstances could yet oblige Mr Romney to take a course that would be less likely to aggravate strategic relations with Russia. If fiscal troubles in the US prompted cuts in the defence budget beyond those currently planned, the administration could opt to spare conventional capabilities and procurement by reducing the nuclear force. Owing to the age of a large part of its nuclear arsenal, Russia is likely to embark on this course. Thus it is possible that both states might engage in nuclear-force cuts that would maintain a rough parity and offer some reassurance to each other.

Middle Eastern crises

The current US position on Iran's nuclear programme and the Syrian civil war is to work within the UN Security Council on the use of force, while using other forums and relationships to put economic pressure on Iran and Syria. Russia has stood against these efforts, but it has also ceased supplying weapons to Iran and Syria. Ultimately, Mr Obama may resort to military action. The main question for a prospective Romney presidency is whether that possibility becomes more likely. Instituting a no-fly zone in Syria or inserting troops would need the support of regional allies, in particular Turkey. A victory for Mr Romney might embolden Israeli leaders to attack Iran-a more plausible scenario than the US initiating military hostilities against Iran. Any resort to force without a UN mandate would seriously damage US-Russian relations.

Commerce and conscience

Russia has joined the World Trade Organisation (WTO), but the US is yet to grant Russia permanent normal trade relations. Moves to do so by repealing the Jackson-Vanik amendment have been stymied by the US election and efforts in Congress to tie such relations to legislation that would punish Russian officials deemed guilty of human rights abuses, including the arrest and death in custody of Sergei Magnitsky, a whistleblower. The Obama administration has taken action against those suspected of complicity in Mr Magnitsky's death, but in a limited and low-profile manner. It is not clear whether Mr Romney would be more forceful, because there are Democrats and Republicans on both sides of the argument. It seems likely that Mr Romney will back granting permanent normal trade relations soon after the election, but he might be more amenable to framing human rights legislation in ways that the Russian political class would regard as unwarranted interference in Russian domestic affairs.

A rockier road

The potential impact of a Romney presidency on US-Russian relations could be significant, and not only on the atmospherics of the relationship. Changed circumstances mean that the traditional Russian preference for dealing with Republican rather than Democrat presidents no longer holds. There would be little of the spirit of the "reset" launched by Mr Obama. A change of US administration could have adverse effects for political and commercial exchanges between the two states. It is also likely to give impetus to Russia's desire to develop closer ties with rising powers in Asia, as well contributing to a narrative that portrays Russia as targeted by malevolent, interfering Western powers.

At the same time, the potential impact of a Romney presidency should not be exaggerated. Mr Romney is not an ideological politician, and he will have solid reasons to maintain a working relationship with Russia. These include reliance on Russian transit corridors to support US forces in Afghanistan to 2015 and beyond, Russia's veto in the UN Security Council, and its potential to act as interlocutor between the US and rogue states. Finally, there is a significant element of uncertainty that stems from the lack of clarity about what Mr Romney, who has often changed his position, actually stands for. In particular, the extent of the influence on him of several competing Republican foreign policy schools (neo-conservativism, populist isolationism, realism, liberal internationalism) is unclear.

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