Fox News/screengrab
Sen. Lindsey Graham (R-South Carolina) interviewed on Fox News.
"I think melted down last night. I think this was the turning point. And I've said that before, but I really believe it," Graham said during a Fox News interview.
Graham, a lower-tier candidate who has repeatedly feuded with Trump, said he was particularly upset with the businessman's attacks against retired neurosurgeon Ben Carson.
Among other things, Trump blasted Carson for his 50-year-old stories of childhood violence, repeatedly declaring that Carson has an incurable "pathological temper." Trump even compared Carson's "pathological disease" to supposedly incurable child molesters.
"So he's a pathological, damaged camper," Trump said during his Thursday speech. "A problem. Then they talk about my tone 'is a little tough.' Give me a break. ... He went after his mother - went after his mother! Think of this. He went after his mother with a hammer at a fairly young age."
Trump was referring to Carson's memoir, "Gifted Hands," in which the retired neurosurgeon described growing up as a troubled teenager before realizing the error of his ways. "I had what I only can label a pathological temper - a disease - and this sickness controlled me, making me totally irrational," Carson wrote.
Trump also questioned Carson's tale of redemption, suggesting that the retired doctor simply went "into the bathroom for a couple hours, and comes out, and now he's religious."
But Graham joked that Trump's comments were offensive enough that the now-famously calm Carson should consider them fighting words.
"What he said about Dr. Carson - if Dr. Carson was ever going to hit anybody with a hammer, it'd be Donald Trump after all the things he said," Graham quipped. "Dr. Carson found redemption in the Lord. He is a good, decent man."
Graham then turned his statement into a broader critique against Trump's lack of foreign-policy knowledge and against Trump's caustic approach to illegal immigration:
Donald Trump is the most uninformed person I've ever met running for president when it comes to foreign policy. He has no clue of what he's talking about. He doesn't understand how to destroy ISIL. … President Obama doesn't have a clue of what he's doing. Don't replace President Obama with Donald Trump; it will get worse, not better.
Mr. Trump's view of the world is really pretty delusional when you look at it. He has no idea what he's talking about. And over time that will take a toll, I hope. If it he doesn't, here's what he's doing: He's building a third term for the Democratic Party in the White House. He's building a wall between the Republican Party and Hispanics. His immigration position is mean, is cruel, is impractical. What he's saying is going to hurt us for generations to come with Hispanics, who should be our voters. And his foreign policy is even more than naive than Barack Obama.
"Other than that," Graham added of Trump, "he's a good candidate for president."