The leading GOP candidates have each received high profile endorsements ahead of the all-important primaries on 15 March.

Actor Jon Voight formally endorsed frontrunner Donald Trump and called on fellow Republicans to do the same while former presidential candidate Carly Fiorina formally endorsed Texas Senator Ted Cruz.

"He's an answer to our problems," Voight told Breitbart about Trump. "We need to get behind him. The Republicans need to unite behind this man. We need somebody to go in and reconstruct us in a sort of way, get us back to where we were, who we need to be." In a statement, the Academy Award winner added: "Donald is funny, playful, and colourful, but most of all, he is honest."

Meanwhile, former GOP presidential candidate Carly Fiorina has put her weight behind Cruz during a surprise appearance in Miami, Fox News reported. The ex-HP CEO called the Texas senator a "leader and a reformer" and encouraged Republican voters to stand behind Cruz as the candidate who can beat Trump.

"Donald Trump and Hillary Clinton are two sides of the same coin," she said. "They're not going to reform the system."

Fox News reported that another former presidential candidate, Jeb Bush, is reportedly meeting with the remaining non-Trump candidates in Florida. Bush will meet Cruz, Florida Senator Marco Rubio and Ohio Governor John Kasich on Friday 10 March. The remaining GOP candidates will meet in Miami for the final debate before the 15 March primaries.

Kasich told reporters he does not know what Bush's plans were and whether he plans to endorse a candidate. "I like Jeb. I've known him a long time and I don't try to pre-guess what's going to happen in a meeting," he said. "Of course I'd like his endorsement. I'd like everybody's endorsement."

The upcoming GOP debate will happen just two days after the 8 March primaries, which saw Cruz take home one win and Trump nab three wins. On 15 March, they will face off in several states, including Rubio's home state of Florida and Kasich's home state of Ohio.