The campaign logo is ready, so is the big speech, and his message is taking shape: Jeb Bush is about to join the crowded Republican field running for president in 2016.

Bush, 62, has run a de facto race for six months, raising money and increasing his travels, including a trip this week to Europe.

On Sunday, his campaign released his logo. It reads "Jeb!" in big red letters on a white background, with 2016 in smaller blue lettering underneath the name.

"I think the transition to a candidacy will allow me to be more direct about my advocacy of the leadership skills necessary for the next president to fix a few things," Bush told CNN in an interview aired on Sunday, a day before his planned announcement in Miami.

"And as a candidate," he added, "I’ll be more specific on policy."

A Bush campaign video lists reforms he made while governor of Florida from 1999 to 2007.

"The barriers right now on people rising up is the great challenge of our time," Bush says in the video.

"My core beliefs start with the premise that the most vulnerable in our society should be in the front of the line, not in the back, and as governor I had a chance to act on that core belief."

Bush aims to break from the pack of potentially 15 or more Republican hopefuls by portraying himself as an experienced executive leader not tainted by Washington politics and the dysfunction that many Americans associate with politics as usual.

But evidence of Bush’s struggle is apparent in Iowa, the state that votes first in the primaries and caucuses that determine the party nominees, and where he finished seventh among declared or potential candidates in a poll last month.

Nationally, Bush is bunched at the top of most polls, but he is not the dominant figure in the race that many had expected.

In a RealClearPolitics poll average, he leads with 11.3 per cent. But six other Republicans are within just four percentage points, including Wisconsin Governor Scott Walker, who topped the Iowa poll.