In 2002, the Bush administration was met with scant resistance from the mainstream media or wider establishment as it drummed up the case for toppling Saddam Hussein’s regime in Iraq. But there were a handful of dissenters, above all Brent Scowcroft. The two-time former national-security adviser (under Gerald Ford and George H. W. Bush) urged the nation to consider the law of unintended consequences — and to open its imagination to nightmare scenarios…