Did Obama try to delay a deal for withdrawal?

This story has been around in various ways, but this one seems a lot more concrete. Particularly by the amount of people who won't comment.

At the same time the Bush administration was negotiating a still elusive agreement to keep the U.S. military in Iraq, Democratic presidential candidate Barack Obama tried to convince Iraqi leaders in private conversations that the president shouldn't be allowed to enact the deal without congressional approval.

If true, it not only makes Obama the worst opportunist around, but a dangerous man to the US.