The recent targeted attacks on police in Dallas and Baton Rouge have law enforcement on edge. Some departments are telling officers to patrol in pairs when possible, and to be extra vigilant about possible ambush.
Complicating matters is the question of how to interpret and react to the presence of a gun. With more Americans now exercising their legal right to carry firearms, police find themselves having to make rapid judgments about whether an armed citizen is a threat.
While police are more sensitive to the presence of legal guns now, the dilemma isn't a new one. Gun rights groups started a push for more permissive laws in the 1990s, and most states now allow concealed carry, open carry or both.
And police are divided: Chiefs tend to favor more gun control, while the younger rank and file tend to support gun rights.
But even many rank-and-file cops want some limits. Steve Loomis is head of the biggest police union in Cleveland — he calls himself a "Second Amendment guy," but on Sunday he asked Ohio Gov. John Kasich to limit the state's open-carry law during this week's Republican convention.
Loomis, talking to a reporter from The Plain Dealer, said there are certain practical problems in having people walk around downtown carrying semiautomatic rifles.
"Somebody's going to be watching, there's going to be multiple police officers watching that person with that AR-15, when they should be over here watching for the guy that's not on his meds that has a couple of handguns," Loomis said.
That's one of the challenges for police: Even in states with open carry, when people see someone with a gun, they tend to call the cops — and then the police get the thankless job of challenging someone who may or may not be a threat. One high-ranking officer in Texas calls it a "headache."
"When you have all these people running around with guns and rifles, you don't know who the bad guy is," he says.
Another potential headache is concealed-carry permits, and the people who like to keep their guns secret, like Joseph Olson of Minnesota.
"Unless it's an essential part of what I'm doing, like defending myself, whether or not I'm carrying it at any given time is something I never say," says Olson, a retired law professor who led the campaign to make his state a concealed-carry state in 2003.
Legal guns used to be a rarity in the Twin Cities, but in recent years the number of permits has jumped, and armed citizens are a routine factor for the police.
Olson says he thought Minnesota police had adapted to the reality of legal guns — until he was pulled over by an especially nervous-seeming cop.
"His voice had a tremor in it and I remember thinking to myself, 'Oh, my God.' I decided when I heard his voice that I was not going to introduce another element into the transaction," Olson says. He decided not to mention his gun.
Minnesota law doesn't require people to tell police they have a gun unless asked. Instructors give conflicting advice on this — but cops say they appreciate being told as soon as possible. Most of them have stories about close calls, when a legal gun appeared in the wrong way.
One officer recalls telling a gun owner, "Do you realize you almost died tonight?" The officer, whom we're not identifying because he doesn't have permission from work to talk about this, says he'd pulled the man over for a routine traffic stop.
"So I said, 'I see you have a permit to carry. Do you have a firearm in the vehicle?' "
"And ... [he said] 'Yeah, it's right here,' and he reaches over to his passenger seat, and I'm going, 'Stop. Don't move,' and he grabs this shirt," the officer recalls. "And I can then see a gun in it, and he's grabbing it."
The officer says he managed to grab the man's arm before being forced to pull his own gun, but police have shot motorists for a lot less than that.
Minnesota is an example of a state that's still adjusting to its new gun culture, and the state hasn't introduced any specific training for officers on how best to handle legally armed citizens. Some wonder if that played a role in the death of Philando Castile earlier this month. He's the black man who was shot during a traffic stop; his girlfriend, who was in the car with him, has said he was trying to tell the officer about his permitted gun.
Scott Dibble, a state senator from Minneapolis, says he's surprised officers haven't been given specific training for these situations, and he's also concerned that members of the public aren't being given clear, consistent instructions on how to inform officers that they're armed.
Dibble favors maximum transparency: "Seems like the right thing to do is to say, 'Officer, I'm a concealed-carry permit holder, I have a firearm, I don't want you to be surprised should you see it.' "
Then again, Dibble says, that's apparently what Philando Castile was trying to do when he got shot by a police officer.