In late 1950 the Chinese managed to sneak an army into north Korea and surround X corps. This was a bit problematic, as you can imagine. MacArthur's staff had vehemently denied that the Chinese would get involved, and when reports of Chinese assaults were relayed, Willoughby (MacArthur's Chief of Intelligence) snorted "That's another goddamn Marine corps lie". There were a lot of internal politics involved and MacArthur did not want to believe that the Chinese had entered the war. Reality tends to trump politics though.
Chesty Puller was commanding the 1rst Marine Regiment at the time. When the embedded press asked him about his plans concerning the distressing situation they were in it's reported that he replied;
"We've been looking for the enemy for several days now. We've finally
found them. We're surrounded. That simplifies our problem of finding
these people and killing them."
It is also told that when informed by his intelligence staff that they were surrounded, he quipped;
"Great. Now we can shoot at those bastards from every direction."
The order was given for X Corps to turn around and march back down to Hungman, to establish a perimeter under the guns of the Navy. Puller's regiment, acting as rearguard for X Corps, not only smashed up 7 Chinese divisions on their way out, but managed to take a bunch of equipment the Army had abandoned. When they reached the safety of Hungman, Chesty told some reporters, "Remember, whatever you write, this was no retreat. All that happened was that we found more Chinese behind us than in front of us, so we about-faced and attacked".
I bring all of this up not only because it's fascinating history, or that brave men and their deeds should not be forgotten, but to highlight that Puller was not "nervous in the service" so to speak. He wasn't prone to exaggeration or paranoia or unwarranted concern. In fact the actions mentioned above got Chesty his fifth Navy Cross and a Distinguished Service Cross from the Army.
On the road from Koto-Ri to Hungman, Puller admonished his troops, especially the tank commanders, to not let the civilians that were tagging along get too close. Most were merely North Korean refugees that just wanted to get the hell out of there and find some semblance of safety (and food and shelter). But scattered among them were North Korean and Chinese soldiers that had donned civilian clothing. Under their coats they had grenades and submachine guns. The instructions were to fire over the heads of the civilian crowds to keep them back. If that failed then firing into the crowds was the only thing to do. It was gruesome and a sorry thing to go through, but necessary. A few commanders didn't follow those orders and at least 3 tanks were lost because of it.
When talk of bringing refugees from the middle east over here comes up, I recall what Puller went through in North Korea. I remember the unwillingness of the brass to acknowledge the realities of the situation, and the danger that was hidden amongst folks that were naturally sympathetic.
The reality is that for every hundred or thousand refugees that only want a safe place to live there's probably a few miscreants who wish to get as close as they can before they attack. It's entirely possible, given the relatively porous state of our borders, that dozens of such infiltrators are already here, waiting for the moment to strike at us. But I see no benefit in flying more groups in here when they're possibly contaminated by those who only want to get their jihad on.
The federal government here is even blinder than MacArthur's folks back then; the current administration will refuse to see beyond the politics of the situation and thus dismiss the notion that they cannot control every single immigrant once they're here.
Being vigilant is definitely something to strive for (as it always has been). This country has plenty of soft targets - schools, malls, movie theaters - too many of which are "gun free zones". This country has plenty of places where self defense and effective tools for same are discouraged. If you have to be in any of those locations I'd advise keeping your eyes open as well as having a plan to deal with any sudden jihad syndrome that infects the place. With the holidays approaching, many of those aforementioned places will be much more crowded than usual, and thus be more tempting targets as well as being harder to notice signs of danger in.
If several places are hit on the same day across the country it'll create a panic. I'm confident that in such an event the federal and state governments will take immediate, decisive and inarguably wrong steps, bolstered by folks who are just downright scared. The upshot of this cheery prediction is that, as you probably already figured out by now, you're on your own.
So have a plan, not just for dealing with a crackhead who really needs your money and has a knife to prove it, or for some emo punk that thinks killing folks before offing himself is somehow the thing to do, but for being in a place that has 2 or more attackers that desire to punish the infidels in as great a number as possible before moving on to the next location on their quest for religious purity. I'd go ahead and assume they would have something thicker and more bullet resistant than a T-shirt on under their coats, for what it's worth. (If you're thinking, "Gee, it'd sure have been nice if they hadn't outlawed armor piercing handgun ammo now wouldn't it? then allow me to welcome you to the Libertarian Party).
That means having an escape plan, and having the means and skills to fight back if escape isn't desirable or feasible. Some folks suggest putting the trunk gun back in your trunk, though I'm still wondering why anyone would drive around without at least one there in the first place. If you can't keep a medical kit on you, at least have one in your vehicle. And for Vishnu's sake, don't walk around in a blissful daze thinking your I-phone's screen is more important than your surroundings. If you end up in Valhalla because you were reading a semi-funny text and didn't notice Jihad Joe whipping out an AK and deciding you were a perfect first target, Thor will make fun of you. For millennia.
I'll leave you with another admonition from good ol' Chesty:
"I want you to make 'em understand; Our country won't go on forever, if we stay as soft as we are now. There won't be any America - because some foreign soldiery will invade us and take our women and breed a hardier race."