When President Barack Obama welcomes the presidents of Pakistan and Afghanistan to the White House on Wednesday, he will be meeting two leaders the US relies on – and deeply distrusts.

The Americans desperately need both Hamid Karzai of Afghanistan and Asif Ali Zardari of Pakistan to get a grip on the deteriorating security situation in the region now referred to in Washington as “AfPak”. But both men are regarded as incompetent leaders with whom the US has a scratchy and difficult relationship.