McSally made the remark about rival Kyrsten Sinema during Monday night's Senate debate.
"Arizona deserves better," wrote Giffords on Twitter Wednesday morning. "Throwing around serious charges just to get a leg up on a political opponent in an election is irresponsible and dangerous. We need leaders who understand that words matter because words lead to action."
The "treason" moment injected a new line of attack for McSally. With the race essentially tied, it provided her a breakout moment on the national stage just days before her most prominent cheerleader, President Donald Trump, headlines a "Make America Great Again" rally for her in Mesa.