US presidential race: Donald Trump leads Republican field as Ohio governor John Kasich becomes latest contender

Poll puts tycoon ahead of the field with 24 per cent support against 13 per cent for his nearest rival, Scott Walker

John Kasich announced he will be running in the Republican Party's nomination race at Ohio State University on Tuesday (AP)

Governor John Kasich of Ohio became the 16th – and presumably the last – serious contender to join the overflowing field of Republicans seeking the White House, hoping to find oxygen in a nomination race that has suddenly been turned upside down by the insurgent candidacy of Donald Trump.

Mr Kasich, 63, has often strayed from conservative dogma – for instance by accepting extra Medicare funds under the Obamacare act – and hopes to set himself apart as an experienced pragmatist in what is now the most wide-open scramble for the Republican nomination in modern times.

“I have the experience and the testing which shapes you and prepares you for the most important job in the world,” said Mr Kasich, who spent 18 years in the House of Representatives and was a managing director of the now defunct Lehman Brothers bank. “The sun is going to rise to the zenith in America again. I promise you it’s going to happen,” he said.

But even as he announced his candidacy, Mr Kasich faced competition for media attention from Mr Trump, who was addressing supporters in South Carolina.

The tycoon has come under widespread attack for smearing Mexican immigrants as rapists and drug dealers and questioning the war record of Senator John McCain.

“I’m a little strong, they don’t like it,” he said of his detractors. Mr Trump took aim at Senator Lindsey Graham, who had called him a “jackass” for his comments. “What a stiff… by the way, he’s registered zero in the polls,” he said.

A Washington Post-ABC News poll showed Mr Trump ahead of the field with 24 per cent support against 13 per cent for his nearest rival, Scott Walker, the Governor of Wisconsin. Meanwhile, in the key caucus state of Iowa, the Des Moines Register called Mr Trump a “feckless blowhard” and demanded that he get out of the race entirely.