After weeks of speculation about his failing campaign for U.S. president, Herman Cain finally stepped up on Saturday to answer the question: Will he stay or will he go?

With his poll numbers in freefall and his campaign donations dried up, Cain told a gathering of supporters in Atlanta that he has suspended his race for the Republican presidential nomination.

"I am suspending my presidential campaign because of the continued distraction (of various sexual allegations)," he said. "(But) I am not going to be silenced and I'm not going away. … I will continue to be a voice for the people."

For weeks, Cain has been dogged by a string of sexual harassment allegations and a claim of a 13-year extramarital affair.

The Georgia businessman, who once ran Godfather's Pizza, has seen his candidacy rise from longshot to front-runner, then tumble back down to little more than tabloid fodder in a matter of months.

Cain's bid for the presidency was seriously harmed in October when it was revealed that the National Restaurant Association had paid settlements to two women who had claimed that Cain had sexually harassed them while he was the organization's president.

The damage continued when two more women came forward to make similar claims against him. Cain denies all the allegations.

Perhaps the final straw came on Monday when 46-year-old Ginger White told reporters she and Cain had been in a relationship for 13 years. Cain denies that as well.

On Friday, Cain came home to Atlanta and saw his wife for the first time since Ginger White went public.

"My wife and family comes first," Cain told reporters. "I've got to take that into consideration."

Ever since his campaign floundered, former speaker of the House of Representatives Newt Gingrich has taken over as the main rival to former Massachusetts governor Mitt Romney in the race to become the Republican flag bearer against President Barack Obama next November.

But even while Cain attracted popular support with his 9-9-9 tax proposal – 9 per cent income tax, 9 per cent business tax and 9 per cent national sales tax – he often slipped on policy questions.

The Republican candidates will face their first real test with voters in the Iowa caucuses next month, and it is in that state that Cain's sliding support was most evident.

Just a few weeks ago, Cain was at 23 per cent support among Iowa voters. By this week, his support had plummeted to 8 per cent.

In his speech in Atlanta on Saturday, Cain delighted the crowd by telling them that with the man in the White House and the two Republican front-runners, he had made the Final Four.

"This is a great nation," he told the cheering crowd with his wife in the background. "I am proof a common man could lead this nation."

Cain promised that while he may no longer be a candidate to bring change from inside the White House, he will work in an as-yet unclear way to bring change from the "outside."

"I am not going to be silenced," he said. "And I am not going away."

With files from The Associated Press