Americans tend to choose presidents who differ from their predecessors, regardless of whether they come from different parties or from the same party.

That’s readily evident in comparing Bill Clinton with George W. Bush or Bush with Barack Obama. But it was also true for the first George Bush, who promised and delivered an administration “kinder and gentler” than Ronald Reagan’s, though they were both Republicans who agreed on most issues.

Now, as Hillary Clinton gives every sign of running again in 2016, one of her biggest challenges may be to overcome the indication in polls that Americans want something very different from President Obama. Her options are limited, since she is unlikely to join leading Republicans in urging dramatic policy changes such as repealing or significantly changing the Affordable Care Act or challenging Obama’s basic economic and social policies.

In recent weeks, the former secretary of state has illustrated their stylistic differences by advocating a tougher tone toward Russia and the Middle East. And she has shown signs she would try to tackle a leading goal of party populists unhappy with Obama, the growing economic inequality exacerbated by the Great Recession and its lingering aftermath.

More immediately, her speech at Sunday’s Harkin Steak Fry in Indianola, Iowa, underscored her need, if she runs, to add substance to the basic election choice she outlined there: “the (GOP) guardians of gridlock and the champions of shared opportunity and shared prosperity.”

“It is true I am thinking about it,” she acknowledged to the crowd, many wearing “READY” T-shirts. “But for today, that is not why I’m here. I’m here for the steak.” Judging from some comments from wary Iowans, her 2016 agenda will first need to answer the question that exemplified another Democratic campaign some three decades ago, “Where’s the Beef?”

When she does, however, her policy pronouncements are unlikely to display greater substantive difference with Obama than the more superficial and stylistic ones already evident.

In an age where visuals count, the fact that she is a white woman, hoping to succeed an African-American man, may well affect those two influential political constituencies. But there are clear differences of style.

He is a cautious intellectual who has proved better at developing policies than selling them. She is blunter and more politically attuned to the necessity of cultivating political relationships to achieve substantive goals.

She showed that in both the Senate and the State Department and, in a CNN Town Hall in June, used words that seemed clearly designed to contrast those differences. “Some people can paint a beautiful vision,” she said. “And, thankfully, we can all learn from that. But then, can you, with the tenacity, the persistence, the getting-knocked down/getting-back-up resilience, can you lead us there?”

In another speech, she recalled how her husband dealt with a Republican Congress. Though it twice shut down the government and impeached him, “Bill never stopped reaching out to them.”

Obama has done that far less, complicating enactment of important legislative proposals.

Timing also might help show a subtle difference between them. By agreeing to become his secretary of state, she bolstered both his presidency and her future, ensuring party unity past the next election.

She shared in some of his more significant first-term successes, the winding down of the Iraq and Afghanistan wars and the capture of Osama bin Laden, a mission she favored and a potential rival, Vice President Joe Biden, opposed.

But she was gone when his second-term problems arose, including those - with Russia and Syria - where she already had indicated she favored a different policy.

If the 2016 choice is seen as either a third Obama term or something different, polls indicate Americans would favor the latter. So the more that Hillary Clinton can sell the idea she represents a change from President Obama, without alienating his base, the better her chances.