They share a border, but more than that, Iran and Afghanistan share the ability to provide a severe headache for the coalition government. Afghanistan is an increasingly divisive topic in Parliament. The exchanges last week in the Commons revealed that there are both Conservative and Labour MPs, most notably Paul Flynn, who are publicly prepared to argue that the UK should "bring the troops home before Christmas", forgetting that this expression became firmly discredited when uttered in the summer of 1914.
But to leave the connotation aside, the intention is clear: we should bring an end to our operations in Afghanistan as soon as possible, and certainly before the scheduled and publicly announced date of the end of 2014. Both the Defence Secretary and Foreign Secretary were quick to restate the 2014 date for withdrawal, and to reiterate that the Government would adhere to its programme of training Afghanistan forces to assume responsibility for security.
So where does this leave the Government? It is naive to suggest that, even if we began today, we could be out by Christmas. Withdrawal of nearly 10,000 troops and their equipment is not achieved by waving a wand. During any withdrawal, forces are at their most vulnerable. What additional protection measures would be required? What equipment would we be able to bring home? What equipment might fall into the hands of the Taliban? Unless you can answer these questions, talk of early withdrawal makes no sense and could be very dangerous. Rightly or wrongly, the Afghan operation has been conducted in close collaboration with the United States, and we have consistently said that we will leave together. What impact would a departure from our agreement have on our alliance with the US?
The longer we train their security forces, the better chance the people of Afghanistan will have. The bald truth is that we cannot eliminate the possibility of more casualties, and no one believes that Afghanistan will become a model European-style liberal democracy. But without the joint presence of UK and US forces, the chances of achieving sufficient stability to allow the people of Afghanistan to make a choice about their future will be reduced. It is painful to say, and to see, but we have to hold the line until 2014.
Iran poses a headache of a different kind. And once again our relationship with the US will be one of the determining factors. It is self-evident that no other relationship will be more significant than that of the US and Israel, and that between Barack Obama and Benjamin Netanyahu. The deterioration in the latter, and the more cautious expressions of opinion from within the White House and the State Department suggest that unquestioning US support for an Israeli strike can no longer be taken for granted.
Added to which there are increasing signs that some in Israel are questioning the wisdom of such a strike, not least on practical grounds. They have in mind the limited range of Israeli aircraft and the need for tanker support, the difficulty of identifying targets and the prospect of complete success: there is a risk of large-scale Israeli civilian casualties by acts of terrorism in response.
But Obama walks a dangerous electoral tightrope, at least until the presidential election in November. In the US, 75 per cent of Jewish people normally vote Democrat. A large part of the population of the state of Florida is Jewish. Florida is a swing state which, with others, will determine the outcome of the presidential election. Whatever his irritation with Netanyahu, Obama cannot risk alienating the votes of Jewish electors. Hence his equivocal response and refusal to set down "red lines" for Iran at Netanyahu's request.
William Hague, the Foreign Secretary, says that all options for dealing with Iran remain on the table. Understandably, he declines to accept any questions based on the hypothesis that Iran had a military nuclear capability and what the response should be. It would be by no means easy for the coalition government to obtain parliamentary endorsement for military action against Iran, whether by Israel alone or with US support. Once again, the impact on our relationship with the US would be an issue, as well as the threat of terrorist attacks against UK citizens at home or abroad. Any credible plan to contain and deter a nuclear Iran could be decisive in that debate.
To support or not to support a military strike is a decision that Obama would not like to have to make – and the same will apply to David Cameron and Nick Clegg (and Ed Miliband). Party management for all three leaders could be fraught, since it is not difficult to see different views within Parliament and within the parties themselves. Different views within the coalition would be difficult to accommodate. It is a decision that dare not speak its name. The truth is that neither of the alternatives is palatable, which is why any realistic proposal for containment and deterrent would be hugely influential against support for bombing.
For the coalition, domestic politics are difficult, but foreign affairs prove much more problematic.
Sir Menzies Campbell is a former leader of the Liberal Democrats