Miter saw tripping GFCI outlets
I tested my miter saw on a 20A GFCI outlet, it worked fine. I tested my neighbors miter saw on a second 20A GFCI outlet on a second circuit in my house, it also worked fine. But after plugging my miter saw into the 2 indoor 15A GFCI outlets, it would trip the GFCI the moment I started the saw. My neighbor reported a similar problem when he plugged his miter saw into my outdoor 15A GFCI outlet.

So, while it could have been a short, and tripping a GFCI is often evidence that there is something (dangerously) wrong with your power tool, for me the solution was to replace the 15A GFCI outlets with 20A GFCI outlets (on a 20A circuit). Both saws are working fine now.