As Barack Obama begins his second presidential term, much of his focus inevitably is on domestic concerns and the state of the US economy. But in his State of the Union address last week, Mr Obama still found time to press ahead with one of his signature foreign policy goals: the need to push through more cuts in American and Russian nuclear weapons. Making fresh reductions in US and Russian nuclear stockpiles will be much harder now than it was in the first Obama term. But the president is right to make the effort.

Three years ago Mr Obama and his then Russian counterpart Dmitry Medvedev signed the New Start Treaty. Each side pledged to have no more than 1,550 deployed nuclear warheads by 2018. Now the White House wants to go further and bring those numbers down by another third, to about 1,000 on either side.

There are three reasons why it is important to try and make more cuts. First, the US is having to make big reductions to its defence budget. As a result, the cost of maintaining its huge nuclear arsenal looks increasingly burdensome.