BLUFFTON, S.C. — Republican Presidential candidate Donald Trump has pulled a classic adolescent prank on a rival who dared to criticize him, a bit of payback reminiscent of writing the phone number of a nemesis on a wall with the message “Call me.”

After Sen. Lindsey Graham called Trump “the world’s biggest jackass” during a television interview, the billionaire developer read Graham’s personal cellphone number and showed it to TV cameras at a campaign event. Graham joked that he would have to buy a new phone. His voice mail quickly filled up.

The back-and-forth is the latest chapter in an ongoing feud between Trump and those who criticize him. He is now at odds with much of the Republican establishment after a series of incendiary comments, topped by his weekend mocking of Arizona Sen. John McCain’s experience as a tortured prisoner of war in Vietnam.

Since then Trump has intensified his criticism of McCain and his record on veterans issues in the Senate, even as politicians from both parties and veterans groups have rushed to McCain’s defense.

In a speech July 21 to hundreds of supporters in Bluffton, South Carolina, Trump kept on McCain, accusing him of being soft on illegal immigration. “He’s totally about open borders and all this stuff,” Trump said.

The real estate developer also went after others who have criticized him in recent weeks, implying that former Texas Gov. Rick Perry was unintelligent and former Florida Gov. Jeb Bush weak.

McCain sparked Trump’s temper last week when the senator said the businessman’s inflammatory remarks about Mexican immigrants had brought out the “crazies.” McCain said he would no longer respond to Trump’s comments.

Graham, a McCain friend and one of the 16 notable Republicans running for the Presidential nomination, betrayed the growing exasperation and anger of many in the party when he appeared earlier on CBS This Morning.

“Don’t be a jackass,” Graham said. “Run for President. But don’t be the world’s biggest jackass.”

He said Trump had “crossed the line with the American people” and predicted this would be “the beginning of the end with Donald Trump.”

Trump responded during his speech by calling Graham an “idiot” and a “total lightweight,” then held up a piece of paper and read out the senator’s cellphone number to the capacity crowd of 540 people and the TV audience.

He said Graham had given him the number several years ago when he’d asked him to put in a good word with a morning news show. “Give it a shot,” Trump encouraged. “He won’t fix anything, but at least he’ll talk to you.”

Graham’s voice mailbox was full July 21. Spokeswoman Brittany Brammell confirmed the number was his. Graham tweeted later: “Probably getting a new phone. iPhone or Android?”

Trump also ordered the American flags on his U.S. properties to be lowered, an act he said was to honor the five service members killed in last week’s shooting in Chattanooga, Tennessee.

The symbolism served, too, to underscore his claim that he has been a stronger supporter of veterans than McCain, despite the Senator’s central work in passing laws that overhauled the Department of Veterans Affairs and strengthened programs against suicide by service members.

Elsewhere in South Carolina, one of Trump’s rivals, Bush, walked a fine line, criticizing his fellow candidate’s rhetoric on immigration and McCain but saying Trump’s supporters are “good people” with “legitimate concerns.”

“I respect the sentiments people feel when they hear Trump talk. The problem with Mr. Trump’s language is that it’s divisive, it’s ugly, it’s mean-spirited,” Bush told a gathering of Republican women in Spartanburg. “We have to separate him from the people that have legitimate concerns about the country.”

Another GOP rival, Rand Paul, was more dismissive. “People have to decide what’s more important in trying to fix the country — real solutions or bombast,” said the Kentucky Senator. He predicted the GOP campaign will “get beyond the novelty of a reality TV star.”

The back-and-forth is the latest in a series of showdowns between Trump and fellow GOP candidates frustrated by Trump’s brash campaign, which has often overshadowed their own in recent weeks.

In his speech, Trump brushed off the criticism he’s faced, both from political rivals and others angered by his comments.

He said he’s had business success even with countries he’s criticized, such as China, and negativity doesn’t affect him. He also said his wealth insulates him because he’s not beholden to donors who might not like what he says.

While his sharp tone has been criticized by Republicans and Democrats, including Senate Democratic leader Harry Reid, he said, “We need enthusiasm. We need tone.”

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By Meg Kinnard and Jill Colvin. AP writers Bill Barrow in Spartanburg, South Carolina, and Jonathan Lemire in New York contributed