PHILADELPHIA — With the primary elections long past and the partisan cheers of July’s party conventions fading away, it’s “game on” for presidential hopefuls Hillary Clinton and Donald Trump.

And both candidates have to plot a course to victory while most American voters don’t much like either of them. Trump is viewed unfavorably by a startling 57 percent of American voters, according to the RealClearPolitics poll of polls. But Clinton fares just a tick better, at 56 percent.

“The next president could be the candidate voters dislike the least,” said Tony Quinn, a former GOP consultant who now edits the nonpartisan California Target Book. “There is a lot of unhappiness out there.”

But the just-concluded conventions provide clear signs of the very different paths Trump and Clinton hope to take to victory on Nov. 8, just 100 days away.

In a gloomy jeremiad to the Republican delegates at their Cleveland convention, Trump painted a picture of America as a fearful country on the brink, threatened by disasters of its current leaders’ making.

“Our convention occurs at a moment of crisis for our nation,” the New York City developer said. “The attacks on our police, and the terrorism in our cities, threaten our very way of life. Any politician who does not grasp this danger is not fit to lead our country.”

Clinton talked of a country on the rise after years of troubles.

“We are clear-eyed about what our country is up against,” the former secretary of state said. “But we are not afraid. We will rise to the challenge as we always have.”

Those competing views of America are likely to dominate the fall campaign, said Henry Brady, dean of the Goldman School of Public Policy at UC Berkeley.

“Clinton must acknowledge that people are feeling angry and then turn lemons into lemonade,” he said. “Trump has focused on the lemons.”

The question for Trump, though, is whether fear is enough to win an election, Brady said.

“Is there an upper limit?” he asked. This year, “some voters are so propelled by fear and anger that they’re just glad to have a candidate who will make major changes.”

If the angry GOP conservatives at the Republican convention and the disappointed progressives who backed Vermont Sen. Bernie Sanders for the Democratic nomination are both calling for a president who will blow up the political status quo, a candidate looking to win has to bend to that prevailing breeze.

Trump, in his first run for political office, can easily take up the mantle of Howard Beale, the “mad prophet of the airways” in the 1976 movie “Network,” throwing open the metaphorical window and shouting, “We’re mad as hell and we’re not going to take this anymore.”

But for Clinton, it’s not that easy.

Speaking at the convention Tuesday, Bill Clinton pitched his wife as “the best darn change-maker I’ve ever met in my entire life.” But selling that makeover is going to be hard for someone who has spent a lifetime in public service — and who voters don’t trust very much.

“All of a sudden (Clinton is) for free college tuition and a $15-an-hour minimum wage,” positions pushed by Sanders, said G. Terry Madonna, director of the Center for Politics and Public Affairs at Franklin & Marshall College in Lancaster, Pa., and director of the school’s respected poll. “She’s an establishment candidate, running as part of the political class, but they have to convince people that she’s a change agent because we’re in a period where people are frustrated and want change.”

Clinton’s move to the left isn’t enough for some Sanders supporters, something she must overcome because so many Democrats voted for him in the primaries. Last week, Jennifer Smith, who backed Sanders, walked around Philadelphia carrying a sign that read “Indict Hillary.” Her husband, Christian, carried another that said, “Over the Hill.” They weren’t sure who they would be voting for in November.

“I’m voting in November,” was all that Christian Smith would offer. “I’ll decide in November. I really can’t believe in Hillary Clinton.”

Trump faces troubles of his own. While he was able to romp past a huge and varied field of contenders in the GOP primaries through the force of his outsize personality, his relentless personal attacks and his appeal to disgruntled conservatives, he’s going to face a new level of scrutiny in his one-on-one showdown with Clinton.

Promises to “put America first,” “build a wall” and “make America great again” all work better as campaign slogans than as detailed policy statements. And while freshness may be a plus among voters eager for a new political face, they’re less happy if that becomes a synonym for inexperience.

“Trump has to convince voters that he’s capable of doing the job of president and that he knows economics and foreign policy,” Quinn said. “So far, Trump hasn’t shown that he knows the stuff or that he’s interested in learning.”

There’s nothing conventional about Trump’s outsider campaign, which is heavy on high-visibility, TV-friendly rallies and news conferences and, at least for now, short on the policy papers, voter registration drives and large-scale volunteer efforts of a typical run for office.

It’s an effort focused not on policies, but on him and Clinton, whose legacy, he said in his acceptance speech, is “death, destruction and weakness.”

By contrast, he is running his campaign as the law-and-order candidate, who says, when it comes to what he and his supporters see as a rigged political system, “I alone can fix it.”

There’s no precedent for the type of one-man show Trump is running, said Brady, the UC Berkeley dean. But that’s been the story of Trump’s effort since the day he announced he was running for president.

“Trump is way, way, way behind” Clinton in all the usual measures of running a national campaign, but he doesn’t seem to care, Brady said. “He just seems to believe he can (run his campaign) by making tweets, and so far it seems to have worked.”

At the convention, and probably for the rest of the campaign, Clinton set herself up as the anti-Trump, a wonk from a middle-class family with years of experience who will “sweat the details of policy.” And who also happens to be the first woman ever nominated for president by a major party.

The last day of the Democratic convention featured a stream of independents, Republicans, progressives, military officers, entertainment figures and minority leaders, all enthusiastically endorsing Clinton.

“I will be the president for Democrats, Republicans and independents,” she said in her speech. “For the struggling, the striving and the successful. For those who vote for me and those who don’t. For all Americans.”

It’s a big-tent strategy that Clinton and her team are convinced will overshadow what they see as Trump’s more limited backing. But there’s also the worry that a campaign that promises something for everyone might not provide enough for anyone.

And hanging over the presidential race are polls showing that 70 percent of Americans believe the country is heading in the wrong direction, worrisome news for any veteran politician, but not so much for a political rookie like Trump.

“People are not going to believe everything is hunky-dory,” Quinn said.

John Wildermuth and Joe Garofoli are San Francisco Chronicle staff writers. Email: jwildermuth@sfchronicle.com, jgarofoli@sfchronicle.com Twitter: @jfwildermuth, @joegarofoli