It has been obvious from the start of the 2008 campaign that the wars in Iraq and Afghanistan

are the biggest foreign policy challenges awaiting the next president. But there has been precious little detailed discussion of them on the campaign trail.

Until this week, when Senator Barack Obama, the presumptive Democratic nominee, offered a sensible blueprint for dealing with the mess that President Bush created by bungling the war of necessity against Al Qaeda in Afghanistan, which could have made Americans safer, and starting a war of choice in Iraq, which made the world more insecure. Obama’s Republican rival, Senator John McCain, is no longer able to ignore the situation on the Afghan-Pak border, where Al Qaeda and Taliban — the true threats to American security — are resurgent. But he has not matched Obama’s seriousness on Iraq.

Obama proposed keeping a residual force in Iraq for specific missions like fighting Al Qaeda. The more the US insists it will not even consider withdrawal, the less incentive Iraqis have to settle their political differences. Iraq’s leaders have asked for a withdrawal timetable. The next president needs to take them at their word. The candidates need to keep talking about how they will meet that goal and address the real threats in Afghanistan and Pakistan.