Leading article: Realism makes a welcome return to US foreign policy

The real surprise is that it has taken so long. After five months, President Barack Obama's foreign policy is now under assault, from both left and right. For some liberals, he is little more than Bush-lite. US troops are still in Iraq, they complain, and even more of them are being despatched to fight America's other war in Afghanistan. Guantanamo Bay is still open, complete with revamped military tribunals.

For conservatives, on the other hand, he is a child in a man's world. What, they ask, has been gained by this new approach of engagement and sweet reason? North Korea has exploded a second nuclear device, while Iran, that other member of the Bush-era "axis of evil", has given absolutely no sign of halting its uranium enrichment programme and has now displayed its true face by violently suppressing protest against the scarcely credible result of its presidential election. Mr Obama's harsh condemnation this week of both the treatment of demonstrators and the legitimacy of that vote is merely too little, too late – says the right.

In fact, both sides are wrong. Mr Obama has changed the parameters of American foreign policy, in the Middle East in particular, and the consequences have been immediate. His Cairo address to the Islamic world was a remarkable event in itself; it was followed a few days later by an election in Lebanon that amounted to a defeat for Iran and a victory for pro-Western forces. Well before that, his overtures to Iran had signalled to both the Tehran regime and its opponents that they were not dealing with a President Bush. These overtures, beyond doubt, changed the dynamic of the recent election, and helped set in motion events that have shaken the Islamic Republic to its foundations.

An "Obama effect" is also at work on the most intractable regional dispute of all, the Israeli-Palestinian conflict. His own background has helped: what other president could so powerfully have used the example of the US civil rights struggle to argue non-violence to the Palestinians. Simultaneously, he has warned Israel that settlement expansion must stop, perhaps placing the Jewish state and its key ally on a collision course. Already he has changed some long-held assumptions, if not yet the underlying realities.

But Mr Obama is attempting something else, that offers an equal contrast with his predecessor. Subtly, but unmistakably, he is telling America about the limits of its power. Maybe he would have preferred not to criticise Iran so harshly, knowing that his words would only enable the regime to blame the US for all its ills, and depict its opponents as stooges of "the Great Satan" – in essence the strategy used by Fidel Castro in his half-century of successful resistance to American pressure. But the violence left him no alternative. Not by coincidence, Mr Obama is reshaping Washington's bankrupt Cuba policy as well. In both instances, the underlying message is the same. However much it might wish it, America cannot bend the world to its will.

The process of change will be slow and frustrating, especially to idealists who believed a changing of the guard at the White House would bring success at a stroke. But Mr Obama himself has never been in their number. He believes you must deal with the world as it is, not as you would like it to be. The true lesson of these five months is not that Mr Obama has been too liberal or too conservative. It is that in foreign affairs he is a realist, a gradualist and a pragmatist. Compared with what went before, that is the biggest change of all.