Republican presidential frontrunner Donald Trump continued his attacks on nearest rival, conservative Texas senator Ted Cruz, calling him "a liar" and saying that he has a "mental problem".
As the White House race heads towards the third nominating contest on Saturday – the primary in South Carolina for Republicans and the Nevada caucuses for Democrats – the candidates are stepping up campaigning across both states.
Mr Trump, the brash businessman leading the Republican primary race, has said that he was "very seriously" considering suing Mr Cruz about his eligibility to run for president because of his birth in Canada if the Texan doesn't end attacks against him and "retract his lies".
The New York billionaire has accused the conservative firebrand of misleading voters about his stance on abortion and his position on President Barack Obama’s signature healthcare insurance law.
"Ted Cruz is a liar, Mr Trump told ABC News TV show Good Morning America. "I think he's a very unstable person. I have never had somebody take something you believe in and say the exact opposite."
The tycoon came second to Mr Cruz in the inaugural presidential contest in Iowa but won in New Hampshire eight days later.
Mr Trump again criticised former president George W Bush for the September 11, 2001 attacks yesterday, saying that had the businessman's own immigration policies been in place at the time, the hijackers would not have been in the country "for the most part".
“I don’t know if [Bush] lied or not,” he said.
Mr Cruz on Monday accused Mr Trump of siding with liberal film-maker Michael Moore and "the extreme fever-swamp left wing" in calling for the impeachment of George W Bush over Iraq.
Campaigning for his brother Jeb in a bid to breathe life into his flagging presidential bid, Mr Bush attacked Mr Trump’s name-calling and bombastic campaign without naming the businessman.
““Strength is not empty rhetoric. It is not bluster. It is not theatrics,” Mr Bush told a rally in South Carolina on Monday night in his first appearance for his brother on the campaign trail.
“Real strength, strength of purpose, comes from integrity and character, and in my experience, the strongest person isn’t usually the loudest one in the room.”
A new South Carolina poll of Republicans, by local newspaper The State and Public Policy Polling, showed Mr Trump as the runaway leader with 35 per cent support, followed by Mr Cruz on 18 per cent. Mr Bush is in fifth place with 7 per cent.
The same poll on the Democratic side showed Mrs Clinton with a 21-point lead over her rival, Vermont democratic socialist senator Bernie Sanders, ahead of the state's Democratic contest on February 27th.
Mr Sanders is first trying to erode the “firewall” Mrs Clinton’s team maintains she has in Nevada among Latinos by outspending her in television ads by roughly two to one and appealing to young and working-class Hispanics with his anti-Wall Street message in a state that was badly affected by the financial crisis.
Other ads are not going so well for some candidates. A new TV ad promoting Republican Marco Rubio, promising a return to "morning in America", shows the sun rising over the Canadian city of Vancouver.
Mr Rubio’s campaign told news website Buzzfeed that the use of the clip in the ad was a mistake.
