Southern Republican senators defended Jeff Sessions after an explosive new book by Bob Woodward recounted how President Donald Trump called his attorney general a "dumb Southerner" and mocked his accent.

In Woodward's forthcoming chronicle of Trump's White House, "Fear," he writes that the president privately called Sessions a "traitor," saying: "This guy is mentally retarded. He's this dumb Southerner . . . He couldn't even be a one-person country lawyer down in Alabama."

The remarks are said to have come during a conversation between Trump and his former staff secretary Rob Porter about Sessions' decision to recuse himself from the Russian investigation. They represent the most withering insults the president has directed at his attorney general in their long war of words.

Republican lawmakers are typically cautious in their criticism of Trump's latest remarks, but on Tuesday several senators who said they had not read the book still bristled at the president's alleged slight.

"I'm a Southerner, people can judge my intellect, my IQ, by my product and what I produce rather than what somebody else says," said Sen. Johnny Isakson, R-Ga., in an interview.

"We're a pretty smart bunch. We lost the civil war, but I think we're winning the economic war since then . . . I'm not gonna get into name calling because I don't think you should be allowed to call names - including the president," he added.

Sen. Richard Shelby, who served alongside Sessions during his 20 years as senator for Alabama, said: "Well, I'm sure I've got that accent, wouldn't you think?"

He pointed out that Trump himself relied on Southern voters during the 2016 general election, warning: "I guess the president, he says what he thinks . . . I think the president's probably got a lot of respect for the South, I hope so. He did well there. Without the South he wouldn't be the president of the United States."

Of the 11 Southern states, 10 voted for Trump - with Virginia backing Democrat Hillary Clinton.

Asked what he thought of Trump's claim that Sessions was "mentally retarded," Shelby, the fifth most senior Republican senator, added: "I think that's strong words. I think Sessions is a very smart man and a man of integrity. I would disagree with the president on that."

Sen. James Inhofe, R-Okla., added to the chorus of disapproval, joking that Sessions was not a "dumb Southerner" but a "smart Southerner." "Oh come on," he said. "I'm a Southerner too. I think it's not at all appropriate. It's totally inappropriate."

Sen. Thom Tillis, R- N.C., who grew up in New Orleans and Nashville, Tennessee, among other cities, also raised his Southern origins, saying: "As a southerner, I have to say, Jeff Sessions . . . is bright, studied in the law and well-respected universally by the conference here, I think that speaks for itself. He is bright."

The comments come a week after it was revealed that Trump last month privately revived the prospect of firing Sessions, with whom he has clashed on issues including the Russia investigation and presidential interference in the judiciary.

Republicans in Congress' upper chamber have at the same time softened their rhetoric on Sessions, with some openly accepting he will now be replaced but urging him to stay on until the midterm elections.

Said Bob Corker, R-Tenn., on Tuesday: "I think we all know it's likely he is going to terminate him after the midterms. In the interim I think it would be good if he stopped raving about Sessions. It's unbecoming. Either do something or don't, but these comments just continue to degrade our nation."

"He doesn't have healthy respect for the democratic institutions we have here. I was down in Venezuela back in May and the characteristics are definitely the characteristics you get out there, where you award your friends and criminalize your enemies," said Corker, who is retiring at the end of his term.

Asked whether he thought Sessions could last until the midterms, Sen. John Neely Kennedy, R-La., told The Washington Post: "I don't know. It's not my call, it's the president's."

On Monday, Trump intensified his criticism of Sessions, blaming him for bringing politically inconvenient indictments against two Republican lawmakers: Reps. Chris Collins, R-N.Y., and Duncan Hunter, R-Calif., who were, respectively, the first and second Republicans in Congress to endorse Trump. Sessions was the third. "The Democrats, none of whom voted for Jeff Sessions, must love him now," Trump tweeted.

The White House did not respond to the specific allegation that Trump referred to Sessions as a "dumb Southerner," but said Woodward's new book was based on fabrications as a whole.