I have yet to see an online petition make an actual difference. But here's one related with the PACT Act.
CLICK HERE TO SIGN PETITION
Someone attempted to post dis petition as a comment on here. But site addresses don't automatically turn into clickable links in the comments area. I might as well post dis as a seperate message.
As far as convincing a Senator who already made up his mind, your best bet is to try to call otha Senators who you haven't called yet. Of course, dat's easier said than done when time is short. Just cuz a Senator ain't in your home state doesn't mean you still can't contact him.
CLICK HERE on how to contact all of the otha U.S. Senators.