Also every cop car in America has either a shotgun or an AR-15/Surplus M4 in it, I know I asked about the specifics from an Orono PD officer and basically they try to keep the cruisers all having the same available gear, but each officer had to be certified to use the rifle before they would be allowed to use it. Orono is a unicorn of a police department though, not all are as responsible.

As for why police need long arms, when responding to a situation with an armed and dangerous individual, police need to have as much or more lethality as the people they're being called to stop. Pistols are more of a "always available" option in the belt because any call or traffic stop could turn deadly at the drop of a hat, but there's a reason the military doesn't equip infantry with only pistols, they're not actually as good, it's harder to hit your Target with a pistol and there's less "stopping power" to them.

These tools are fine for a typical cop in my opinion if used by someone with two braincells who doesn't jump to bringing out the rifle everytime Becky calls about some dark skinned locksmiths working at her neighbor's door, but we live in a country that is far too protective of shitty officers and promotes a police culture that ousts honest ones.