To listen to the way some Republicans tell it, America is a pretty awful place these days.

“A hell hole,” as Donald J. Trump has put it. Our leaders are “babies” who are “so stupid” they can only watch helplessly as we become “a third-world country.”

Senator Ted Cruz of Texas sees evil menacing America not just from within, like the “tyranny” and “lawlessness” of jailing a county clerk in Kentucky who refused to issue same-sex marriage licenses, but from the outside as well. As he condemned the Obama administration’s nuclear pact with Iran last week, Mr. Cruz warned, “Americans will die.”

These dark diagnoses of the country’s condition have become an especially powerful part of the message sounded by several Republicans seeking their party’s nomination for presidency this election cycle.

Their damning assessments — that the country is diminished and unrecognizable, imperiled by forces foreign and domestic — seem to resonate with voters already feeling angry, alienated and under threat.

Appeals to voters’ insecurities and anxieties have always been part of politics. But what is striking about the current dynamic inside the Republican Party is how pervasive the sense has become that the country is slipping, and maybe irretrievably so.

“You’ve got elements of all the different branches of the Republican Party that see darkness now,” said David Gergen, a former adviser to Presidents Gerald Ford, Ronald Reagan and Bill Clinton. “Social conservatives have been at the forefront of that for a long time. But now the foreign policy and economic types feel like we face serious risk of decline.”

The mood of the country is certainly grim. About two-thirds of Americans believe the country is adrift, according to recent public opinion surveys from a variety of news organizations and independent firms. That sentiment has remained stubbornly high for most of the Obama presidency, with strong majorities of Americans consistently saying the country is on the wrong track for the last five years, according to polling by The New York Times and CBS News.

After years of slow economic growth, stagnant incomes, political dysfunction and worsening threats from abroad, many Republican pollsters and analysts are asking themselves whether there has been a fundamental change in how Americans, historically an optimistic people, now see themselves. And they are wondering whether, as a consequence, 2016 will be a year when voters turn to someone whose message is mainly focused on what is wrong with the country.

“Today, conservatism is much more meanspirited, angry, not optimistic and much more viscerally divisive,” said Matthew Dowd, a former top strategist for President George W. Bush.

The dark imagery emanating from Mr. Trump and others collides with the long-held Republican conviction that a message of optimism and uplift is essential to winning elections and leading the country. That belief also aligns with their view of America as a special and divinely inspired nation, always capable of renewal.

“I believe we’re on the verge of the greatest time to be alive,” says Jeb Bush, the candidate who always boasts about the “joy” that infuses his campaign and whose slogan, “Right to Rise,” implies an upward trajectory for the American people.

Optimism and a sunny spirit came to define Reagan, and in this race, Mr. Bush, Senator Marco Rubio of Florida and Gov. John Kasich of Ohio are trying to channel some of that same brightness.

Mr. Rubio often asks people what nation on earth they would trade places with. After the answer comes back an emphatic “No one!” as it did at a casino in northern Nevada he visited earlier this month, he offers his own cheerful explanation. “Ours is the story of 230-some-odd years of perpetual improvement, of a nation where each generation did what they needed to do to leave the next better off.”

Mr. Kasich repudiates “mad as hell” politics when he talks to voters. “If it takes angry and mean, count me out,” he said recently in New Hampshire.

Despite the country’s challenges, there are signs of improvement: Job growth is up, unemployment is down, and the economy is in vastly better shape than it was eight years ago. Some Republicans worry that a strategy of telling voters, in effect, that things are much worse than they thought is a losing one. They point to how candidates like George W. Bush, who ran in 2000 as the amiable “compassionate conservative,” were almost always upbeat.

“Americans like optimistic brands. We like brands that lead us into the future,” said Alex Castellanos, a Republican messaging strategist who has offered informal advice to several of the candidates running for president this year. Quoting something he said George W. Bush had once told him, Mr. Castellanos added, “Nobody ever bought a product that made them feel worse.”