which is going to be the only possible threat to europe within the next two US electon cycles.
Actually, the greatest threat to Europe now and for the foreseeable future is its continuing stunning ability to suck at any and all forms of military action, and that is best rectified by forcing it into battle and making it recognize how terribly it sucks (see: Afghanistan). It already knows on some level (see again NATO failure in Afghanistan, failure of EU Rapid Reaction Force idea, EU/NATO failure to intervene in Kosovo prior to US intervention, NATO as USSR-speed bump) but Europe is generally helpless on the battlefield without America.
Considering America's in a terrible internal state right now that will take literally decades to fix, and it will continue to get worse before it gets better, it's really not a two-term issue, and if Democrats win, start to actually fix the job and thereby keep getting re-elected, focus is going to be at home, not abroad. Short-term that's no big deal.
Longer-term, Europe gets a nice cozy little economy blanket courtesy of Uncle Sam, but if something goes bad somewhere even near their backyard (see again: disintegration of Yugoslavia) they are more or less up the creek without a paddle, because they can't handle it, and quite frankly neither can America (between having our troops distributed willy nilly and having home-focused reformist Presidents).
The humanitarian thing is also a convenient mirage. I didn't see Clinton in Rwanda, he backed out of Somalia real quick, and it took him awhile to get around to Kosovo. Even bleeding-heart liberals are from the school of realpolitik.

Well, that is, unless Kucinich somehow gets elected... god forbid.