Sen. John McCain's daughter shot back at a protester who was reportedly calling for her father's death.
"This Trump supporter is shouting at protestors: "McCain needs to die now!" journalist David Catanese tweeted from Phoenix.
Meghan McCain later responded to the tweet about her father, a US senator from Arizona.
"I wouldn't wish seeing this about your own father on my worst enemy," she said. "May God help these people who inflict such cruelty in the world."
During the fiery rally in Phoenix on Tuesday night, President Donald Trump also discussed his party's failed attempts to repeal and replace Obamacare.
Defying the wishes of national Republicans, Trump criticized Arizona's two Republican senators, McCain and Jeff Flake. He said he "will not mention any names," but added that Republicans were "one vote" short on a Republican bill to overhaul parts of Obamacare.
McCain was one of three GOP senators who voted against the bill. Trump fumed following the loss, tweeting that the three Republicans let the American people down.
Shifting his attacks to Flake, Trump said "nobody wants me to talk about him. Nobody knows who the hell he is. And now, we haven't mentioned any names, so now, everybody's happy."
This is not the first time Trump has criticized McCain, who was recently diagnosed with an aggressive form of brain cancer.
About two years ago, then-presidential candidate Trump said McCain was not a war hero because he was captured, imprisoned and tortured during the Vietnam War.
The Arizona senator has had a lot to say about Trump as well. He's called his dealings with Russian diplomats "deeply disturbing" and his plan to hike the Defense Department budget "totally inadequate." Not too long ago, McCain described Trump's tweets calling for a ban on transgender service members in the military as unnecessary.