"There is the seductive belief that if only we go "over there" to destroy ISIS, that the threat of homegrown radicalism will be solved."

"It will not."

How Not to Fight Islamic Terrorism - Reason.com: "If we make this attempt with renewed vigor as both candidates are calling for, the result will almost certainly be the increase in the threat of domestic terrorism, not its diminution. It's not hard to understand why. I have spent considerable time on the ground in Afghanistan and Iraq over a 25-year period in both a military and civilian capacity. 

I can categorically state that short of a Nazi-like genocidal wiping out of entire populations, it is militarily impossible to go to these overseas locations and destroy the ideology of violent jihadism. 

Our attempts to do so since 2001 in Afghanistan, 2003 in Iraq, and the numerous places we've used special forces and drone strikes to kill Islamic radicals of various stripes since then has succeeded only in expanding the threat. Our efforts have been much like trying to put out an oil fire with water. It only makes the flames bigger. Longtime diplomat and Middle East expert, Chas Freeman, recently explanied that using military power in this way "radicalizes and creates volunteer recruits for our worst enemies. We need to halt this, not double down on it." 

...

You put out an oil fire by suffocating it. As painfully demonstrated by the San Bernardino attacks last December and the Orlando attacks last week, the threat of radicalized, domestic Islamic jihadism is real and growing. Instead of fighting the threat with means that will only spread its flames, we need to change course and deprive it of oxygen instead. 

First is to stop the bleeding and suspend policies based on the belief that the United States can impose a set of values and a political system of our preference on others alien to it. 

Second, we must do all we can diplomatically, politically, and economically to contain the fire of Islamic radicalism to where it currently burns. Working with allies, friends, and even competitors on areas of mutual benefit can help stop the spread by choking off funds, interdicting resupply chains, and blocking routes by which new radicals join the fight. 

Third, we need to stop making far more enemies than we ever eliminate by suspending the use of targeted killing and bombing terrorist targets from the air. This is the most controversial step because it seems counterintuitive to suggest that we can best battle terrorists by ceasing to bomb them. But overwhelming evidence confirms that such tactics are counterproductive and work against our interests. Instead of bombing, we would use the military to help contain terrorist organizations like ISIS where they currently exist, and then employ new, diplomatic measures that have a chance to undermine the terrorists..."