TAMPA, Fla. — Hillary Clinton has vastly outspent Donald Trump on TV ads in Florida. Her 57 campaign offices dwarf Trump’s afterthought of a ground game. And Trump is deeply unpopular among Hispanics, who account for nearly one in five Florida voters.

Despite these advantages, Clinton is struggling in the Sunshine State, unable to assemble the coalition that gave Barack Obama two victories here, and offering Trump a broad opening in a road to the White House that not long ago seemed closed to him. Trump is pressing down hard to win the state, campaigning in Miami on Friday and in Fort Myers on Monday, after a rally in Pensacola recently.

Recent polls show Clinton is not earning the same support among Hispanics, young people, or white voters that Obama captured when he eked out a Florida victory four years ago in the country’s most hard-fought swing state.

Clinton could afford to lose here and still find other routes to victory. Trump’s electoral map is narrower; he must have Florida in his column. But as the most populous and one of the most racially diverse battleground states, Florida is also a bellwether for the nation: a candidate’s struggles here often are mirrored elsewhere.

Polling in swing states that Clinton once led, prompting predictions a month ago of an Election Day romp, now show Trump closing the gap or slightly ahead, including in Florida, Ohio, Iowa, and Nevada.

“If she underperforms what Obama did in ’12, she’s not going to carry Florida,’’ said Fernand Amandi, a Democratic strategist in Miami. A poll his firm conducted for Univision, released last week, showed Clinton winning 53 percent of Florida Hispanics, compared with the 60 percent who voted for Obama four years ago.

After several weeks in which Trump attempted to sand off some of his rough edges and attacked Clinton for portraying half his supporters as “deplorables,’’ the share of Florida voters who view the candidates unfavorably is now the same for Trump as for Clinton, according to a CNN/ORC poll.

With 20 million people and 10 major media markets, Florida is a place of vast diversity and contrasts that is a challenging puzzle for any statewide campaign.

The traditional playbook has been for Democrats to run up the score in South Florida, with its large nonwhite population, and for Republicans to rack up votes in the conservative northern panhandle.

That leaves Central Florida, and especially Tampa on the Gulf Coast, as one of the state’s most contested swing areas. The booming region has the largest share of registered voters statewide, with one in four voters in Hillsborough County, which includes Tampa, registered as independents.

“The old saying is: ‘As goes Hillsborough County, so goes Florida,’ ’’ said Susan MacManus, a political scientist at South Florida University in Tampa. No candidate since 1960 has won Florida without carrying the county.

Some strategists believe the pool of persuadable voters this year is shallower than in the past, which may explain why the tens of millions in TV ads run by Clinton and her allies in the state have failed to give her a noticeable advantage. (Trump and outside supporters have spent about $8 million.)

Clinton’s bulwark is her vast organizing effort, currently focused on registering new voters and signing up volunteers. But Republicans have not been idle: Field teams working for the Republican National Committee and state party have cut the Democrats’ advantage with registered voters in half since 2012. It is now just 258,000 active voters.

Trump must find a way to turn out a wave of white supporters who are infrequent voters. The campaign concedes that Mitt Romney’s field staff members four years ago drove conventional white turnout in Florida about as high as possible.

But Anna Greenberg, a Democratic strategist and pollster based in Washington, said the ability to increase the white vote in Florida was limited, and therefore Trump could not win the state, given his toxicity among nonwhite voters.