While the threat of nuclear attack emanating from one of the states currently posessing these weapons cannot be overlooked, the most imminent and  likely source of attackis that initiated by  a terrorist organization.  The primary reason that we have spent vast sums of money and sacrificed thousands of lives in Iraq and Afghanistan has been to reduce this threat by attempting to deny these organizations a base of operations.  This has proven effective in the short term by diverting the attention of Al Qaida and others from attack to survival, but at prodigious and unsustainable cost.   Foreign wars whether for political, economic or security purposes have rarely if ever been successful .  This has been demonstrated by the ultimate failure of such leaders as Alexander the Great, King George the third, Napoleon, and Lyndon Johnson.  The opposition has only to retreat, hunker down, hide, and maintain of strategy continual small injuries to its opponent.  then reemerge when the superior force it faces expends its resources and withdraws.  The development of weapons of mass destruction has thrown a new wrinkle into this Equation.   Terror now becomes a significant tactic.  For an organization to use it effectively requires three things; access to the weapon, the resources to deliver it, and the motivation to overcome the difficulties and endure the sacrifices to achieve this objective.  Denial of bases of operation deals with only one aspect of the above and is terribly costly.  Far better to focus on making WMD more difficult to obtain, adopting policies that cut sources ofsupport, and addressing the factors of motivation.