Self defense, but just for the moment. A coup, if that’s what you’re suggesting, wasn’t a possibility.
Accounts vary, but I’ve seen claims that southern sympathizers held those who might interfere at bay by gunpoint while Brooks caned Sumner on the Senate floor.
I was thinking more about lone wolf or duets of armed confederate thinkers, who wanted to break into meetings. Not thinking ‘coup’, thats more military styled takeovers.