The sprawling prison complex at the US naval station by Guantanamo Bay, Cuba – the one that President Obama said he would close down soon after he became President? Do you remember how, just a couple of days into office in at the beginning of 2009, he hardened that promise into a specific commitment? How he signed an executive order that promised the closure, within a year, of this notorious facility?
The unpalatable truth, almost five years on, is that the prison is still there. More than 150 men are still imprisoned within it. Fewer than 100 have left. Of those remaining, very few have been charged with any crime.
This is a sad failure, a scar on the President's record that has unfortunate symbolic significance. Guantanamo, originally called Camp X-Ray, had come to represent the excesses of George W Bush's presidency, a presidency that will always be associated with lawless detention and other violations of human rights.
There are excuses for Mr Obama; his continued inability to fulfil his promise has much to do with his ongoing difficulties with the US Congress. He needs to get far more engaged in sorting out the recalcitrant Congress by whatever means he has available. But the rest of the world is not interested in internal political technicalities. It looks at the President, and sees a man who has betrayed hope. The detainees still languishing at Guantanamo tell the world that US rhetoric is hollow, that it is not a country to be trusted.
Overall, the record of this President in foreign policy is very disappointing, not least in his increasing use of unmanned drone aircraft. The main reason that I and millions of others hoped that he would serve a second term was not really based on his record, which was patchy to say the least. It was based more on fears that his opponent, Mitt Romney, would be a very bellicose President.
I cannot see Mr Obama ever being reckless on the world stage. His main problem is one of passivity. He has been surprisingly supine. He appears, if anything, to be scared of Israel. For example, previous US presidents have been able to influence Israeli foreign policy, usually for the better. This President tends to stand back. His few foreign trips have not been well thought out. He preferred to grandstand in Myanmar when he could and should surely have been visiting the Middle East.
He has been weak in his attitude to the odious regime of President Assad of Syria. I'm not suggesting that he should have backed military moves to remove Mr Assad, but surely he could have done more to try to persuade China and Russia to alter their Assad-supporting stance on the UN Security Council? Indeed it must be asked if Russia and China take President Obama seriously.
Of course US presidents have Secretaries of State to attend to the hard grind of world diplomacy, and in this role Hillary Clinton has had some successes. She has certainly worked indefatigably. But she is about to quit, and in the short term this will make the conduct of US foreign policy look even more vacuous and weak than it does already.
Another major external issue looming for the US concerns its neighbour to the immediate south. Mexico is one of the world's emerging economies, and has almost unlimited potential for sustained and even spectacular growth. But it also has a huge – and very well documented – problem with aggressive and lawless drugs cartels that the state seems totally unable to control. At least 60,000 Mexicans, and probably many more, have died in the country's ongoing drugs wars over the past few years.
The newly-elected president of Mexico, Pena Nieto, may decide to try to appease the cartels, rather than declare war on them, as his predecessor did. Such a policy turnabout could cause huge problems for President Obama. For a long time the US has been relaxed about the regimes to its immediate south and immediate north. To the south, that could be about to change.