1. Actively break the terms of (a law, agreement, etc.): "infringe a copyright".
2. Act so as to limit or undermine (something); encroach on: "infringe on his privacy".
As far as a line in the sand for me... Well I'm sure we can all agree that right now is the time to act through your representatives and groups like the NRA. Anything that requires further action will be evident because there will probably be more than one person participating. Be courteous, be professional, don't give them anything they can stick in our eye later. But right now is the time to talk... My fear is when people around the country stop talking and start planning.
In the words of my old crusty Gunnery Sergeant when we were about to head into Ramadi... "Well the f*ggots in D.C. didn't do their f*ckin jobs again, so Shut the F*ck Up and load your mags. Let them run their F*ckin mouths you just load 'em up and we will show them what getting the job done looks like"
Sorry for the language it's how some Marines talk.
(Disclaimer: Nobody's feelings were hurt when this message was delivered.)