Fighting ISIS could take years and it might fail. But it's necessary.

As we wade back in, it behooves those of us who support military action to be honest about two big things.

First: There will be no clear end. We fought these guys before, when they called themselves Al Qaeda in Iraq. They ruled much of the same territory they currently hold until U.S. forces, in alliance with the Sunni tribes, ran the bastards out on greased rails.

They disappeared into the shadows and stayed there for years, not daring to pop up their psychotic heads until Assad lost ground next door to a ragtag rebellion. We could defeat them all over again this year, and they’ll spring back in 2015 or 2016, perhaps in the same place and perhaps somewhere else.

Just because this is going to be a very long fight doesn’t mean it’s an unnecessary one.

Yes, it’s true, ISIS or no ISIS, there’s virtually no chance the U.S. has the power to turn Iraq or Syria into Belgium. But so what? We don’t have to. All we have to do is back a third faction that can weaken ISIS and Assad so they don’t become even bigger menaces than they already are.