"Thank you for your thoughts on this matter, I didn't read them. Here is a boilerplate statement espousing all the great things about this bill that you specifically criticized in your message to me. Please don't reach out again."
Which is why writing him letters won't help. It's not like we have an alternative we can vote for, and if we primary him then we're evil leftists who want Trump Toomey to win by nominating an unelectable candidate.