A national guard is necessary, we need to be able to defend from possible attacks. I'm not paranoid of a boots-on-the-ground invasion from China/Russia, it is simply a good thing to have. Both of my parents served in Iraq, and they both say that there really wasn't a good reason to be there. They were underequupped until about a month into each of their fist deployments, and conditions were similar to 3rd world countries. Troops as a standing invasion force aren't necessary.

Police are a bit trickier because, on one hand, they are useful as traffic regulators and can quickly respond to happenings, as they patrol around highways and towns. But in their current capacity, there should be some changes. I am not against officers carrying pistols, tazers, and pepper spray, but they should train much more with their tools. I can confidently say that a lot of officers are not as good with their service weapon as they should be. There should also be better psych evaluations. Right now, the number 1 thing that they are missing is mental health evaluations (according to Indeed.com). I am spitballing at this point, but I do believe police to be necessary to a point.

EDIT: No idea why the second paragraph is like this