It was billed by some as a preview of next year's general election showdown - the leading lights of two political dynasties offering duelling speeches from the same stage in the key battleground state of Florida.

But when Jeb Bush and Hillary Clinton arrived at the Urban League conference in Ft Lauderdale on Friday - the first time they have shared a stage since 2013 - only one participant was itching for a fight.

After detailing her close ties to the black community before an audience of civil-rights advocates and minority entrepreneurs, Clinton took dead aim at the man who could someday stand between her and the White House - mocking one of his campaign slogans, "Right to Rise".

"I don't think you can credibly say that everyone has a right to rise, and say you're for phasing out Medicare or for repealing Obamacare," she said.

"People can't rise if they can't afford healthcare. They can't rise if the minimum wage is too low to live on. They can't rise if their governor makes it harder for them to get a college education. And you cannot seriously talk about the right to rise and support laws that deny the right to vote."

Republican presidential candidate and former Florida governor Jeb Bush speaks at the National Urban League's conference in Fort Lauderdale, Florida July 31, 2015. Photo: Reuters

Bush recently said he was in favour of means-testing the government-run programme for healthcare for the elderly, Medicare, and he caused a political furore when he was governor for doing away with admissions preferences for minorities in Florida's universities.

When Bush took the stage roughly an hour later, he declined to return fire on the former secretary of state. Instead, he touted his record in Florida, made his oft-repeated promise to enact policies that will boost US annual economic growth to 4% and spoke of education reform.

"I believe in the right to rise in this country," he said, without reference to Clinton's earlier swipes at the slogan. "And a child is not rising if he's not reading."

His speech was delivered with little of the passion that fuelled Clinton's address or, for that matter, that of Senator Bernie Sanders, another Democratic presidential hopeful.

He received polite applause from the audience throughout, with a few more animated responses, such as when he noted that as governor he helped remove the Confederate symbol from the Florida state flag and "put it in a museum, where it belongs".

The differing tones of the two speeches could be explained by the different goals of the two candidates.

Clinton needs to engage black voters - one of the Democrats' most loyal constituencies. Bush, on the other hand, scores points just by keeping his promise to reach out beyond the Republican base.

The kinds of sharp attacks on Democrats - and President Barack Obama, in particular - that are de rigueur before conservative audiences would fall flat at the Urban League.

Bush, like Clinton, has never been considered a particularly effective orator.

He tends to be best in more informal settings, such as the question-and-answer session that took place after his speech on Friday. When asked how to make government civil rights compliance investigations go more smoothly, his quip had the audience laughing.

"I pretty much know you're a black man," he told Urban League President Marc Moria. "And you pretty much know I'm a white guy, right? I don't need to spend a lot of quality time going through that."

Although Bush stayed above the fray during his appearance on Friday, his campaign communications director, Tim Miller, was quick to offer a retort.

"Clintonesque move to pass over chance to unite in favour of a false cheap shot," he tweeted. "When you have no record of accomplishment to point to..."

There's a bit of irony in Clinton's most recent jabs at her Republican counterpart. Several weeks ago, her husband Bill and Jeb's brother George W posed on the cover of Time magazine as "the most surprising couple in politics".

On Thursday Lanny Davis, a former adviser to Clinton, penned an opinion piece for the Daily Caller, praising the civil tone offered by the Clintons and the Bushes, contrasting it with the bombast of candidates like Donald Trump.

"I have a feeling that if Hillary Clinton and Jeb Bush end up as the presidential nominees of both major parties in 2016 - and that may not be the case - that they will conduct a campaign debating the issues that will make most Americans proud, regardless of the outcome,"

That may yet be the case.

But Clinton's comments on Friday should be considered a shot across the bow for the would-be Republican nominee. When the highest political office in the US is on the line, nice guys - and women - often finish last.