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Liar. Liar. Nuts. Unstable. Liar.

Those words made up the rosary of attacks that Donald J. Trump hung around Senator Ted Cruz of Texas on Monday in Mr. Trump’s first appearance of the day in South Carolina, where he savaged Mr. Cruz as a fraud, ticking through a litany of inconsistencies in his positions on conservative causes and accusing him of saying anything to get elected.

Later, Mr. Trump refused to back off his criticism of George W. Bush — on the same day the former president was campaigning for his brother Jeb in South Carolina.

But it was Mr. Cruz who took the heaviest fire.

“I think he’s an unstable person — I really do,” Mr. Trump said of Mr. Cruz in a free-flowing speech in Mount Pleasant, S.C. “Jeb is just Jeb. But this guy, Ted Cruz, is the most dishonest guy I think I’ve ever met in politics.”

It was a theme Mr. Trump repeated, almost verbatim, at a midafternoon news conference, saying that he had to use the news media to try to stop Mr. Cruz and that he was demanding an apology from Mr. Cruz for lying about his positions — or else he would file suit against the senator challenging his qualifications to serve as president because he was born in Canada.

“We will bring a lawsuit if he doesn’t straighten his act out,” Mr. Trump said.

Instead of focusing on what had been the major political event of the day — a former president campaigning for his brother — Mr. Trump trained his attention on another target.

He mentioned specifically the Cruz campaign’s efforts to spread a rumor that Dr. Ben Carson had suspended his candidacy while Iowa voters were still caucusing.

“What he did to Ben Carson in Iowa was a disgrace,” said Mr. Trump, adding it “affected me, too,” because he believes he lost votes in Iowa as a result.

He also accused the Republican National Committee of failing to fulfill the terms of a pledge he signed not to run for president as an independent if he does not win the party’s nomination. “The pledge isn’t being honored by the R.N.C.,” Mr. Trump said, mentioning the crowds at the last two debates, where he was frequently booed.

In Mount Pleasant, Mr. Trump trashed Mr. Cruz as a false Christian.

“The worst is holding up a Bible all the time talking about how — you’re willing to lie about anything and you hold up a Bible,” Mr. Trump said. “I’m Christian, I’m Protestant, I’m Presbyterian to be exact.”

He said he was speaking out to counter ads by Mr. Cruz, who has focused on Mr. Trump’s past praise for his sister, an appeals court judge, as a potential Supreme Court nominee. Mr. Trump implored the news media to help publicize his attacks on Mr. Cruz, saying it would save him money, adding, “Psychologically, I like to watch my costs.”

In Mount Pleasant, he was more overt, saying, “Who the hell wants to take out $2 million worth of commercials when I have enough cameras back there that can get the word around?”

While Mr. Trump saved most of his fire for Mr. Cruz and George W. Bush, his wrecking-ball performance smashed a few other windows, too. Jeb Bush was mocked for using an exclamation point in his campaign slogan, and, after vowing not to go after Senator Marco Rubio “for being the choke artist,” Mr. Trump mocked the senator’s propensity to sweat, saying that at one debate, “I was standing next to Rubio, and I thought he just got out of a swimming pool.”

Instead of coverage of the Bushes’ campaigning in South Carolina, Mr. Trump sucked up all the news media attention and interest for the afternoon with his instant command of cable news.

Mr. Trump also called Mr. Cruz “a basket case,” and said that South Carolina voters were smart enough to understand the truth.

While Mr. Trump did not bring up George W. Bush, when asked, he mocked Mr. Bush’s “Mission Accomplished” appearance during the Iraq war and pointedly said the country had not been “safe” during the president’s tenure.

“You had him on the aircraft carrier saying all sorts of wonderful things,” Mr. Trump said.

“What does that mean, he kept the country safe after 9/11?” Mr. Trump asked. “I’ve heard that for years.”

Growing sharper as he talked, he said: “What about during 9/11? I was there.” He added: “The worst attack ever in this country? It was during his presidency.”

Praising George W. Bush for what happened after the Sept. 11, 2001, attacks was like saying “the team scored 19 runs in the first inning, but after that, we played pretty well,” Mr. Trump said.

Mr. Trump was pointed on the effect the former president would have on his brother’s campaign: “It would be better for him if he stayed out.”

Mr. Trump was pressed repeatedly as to whether he was saying the former president was responsible for the 9/11 attacks. Mr. Trump sought to keep pressure on George W. Bush without explicitly repeating the phrase “they lied,” as he did in the debate on Saturday, referring to the Bush administration’s claims of the presence of weapons of mass destruction in Iraq.

Mr. Trump’s accusation struck many Republican strategists as perilous to his candidacy in a military-heavy state where the former president is still popular.

“I don’t say anything,” Mr. Trump said. “I’m just saying this — if you look back at your records, you’ll see that there’s tremendous information and the C.I.A. and various other agencies were not talking and they were not getting along and there were a lot of personality conflicts and they all hated each other and we ended up with the World Trade Center, O.K?”

Pressed again about whether he was faulting Mr. Bush, Mr. Trump said, “No, I think we could have had greater vigilance, but I would never say anybody was responsible for that.”

Mr. Trump, meanwhile, insisted he had the right credentials to deal with the rigors of campaigning in a state in which nastiness is par for the course.

“I’ve won many club championships — you have to deal with pressure,” said the real estate and golf course developer.