WASHINGTON >> Suddenly, the biggest year-end development in the race for the White House is no longer Donald Trump’s bombast. It is the reshaped agenda facing every candidate.

Recent terrorist attacks now mean that national security, rather than the economy, is at the center of the 2016 campaign. That’s rare in American presidential politics.

The shift has already damaged the campaign of the soft-spoken Republican candidate Ben Carson; the former neurosurgeon’s poll standing has dropped amid questions about his grasp of foreign policy.

As voting nears in Iowa and New Hampshire, the change could further scramble the Republican race, to say nothing of the general election.

Presidential campaigns typically turn on a version of what Ronald Reagan asked in his 1980 debate against the incumbent president, Jimmy Carter: “Are you better off than you were four years ago?”

Even that year, as Iranian revolutionaries held American hostages in Tehran, voters said the economy would influence their decision more than foreign policy.

“The natural tendency is for any given election to be about domestic issues,” said Mark Mellman, a Democratic pollster who advised John Kerry’s 2004 presidential bid. “It has to be pulled, hard, in the other direction.”

The last election to be pulled hard enough was in 2004, three years after the Sept. 11 attacks. Even then, said Mellman, it took a terrorist massacre in Russia on the eve of the Republican National Convention in New York to “lead people back to a national security focus” and cement President George W. Bush’s advantage with jittery American voters.

The campaign this year began with a focus by both parties on reducing income inequality and lifting long-stagnant middle-class incomes. Then came Paris and San Bernardino.

Public sentiment shifted instantly. In the New York Times-CBS News Poll in early November, a plurality of respondents named the economy as the top issue; in early December, a plurality named terrorism. In the NBC News/Wall Street Journal survey released this week, 40 percent called “national security and terrorism” the federal government’s top priority, while 23 percent said “job creation and economic growth.”

Shifts in the rhetoric of candidates came just as rapidly. In the Republican presidential debate on Tuesday, the changing dynamic led Lindsey Graham, a national security hawk, to utter words previously unspoken in the 2016 campaign: “I miss George W. Bush. I wish he were president right now.”

Whether that decisively reshuffles the deck of candidates cannot be forecast. Trump has defied predictions that his brusque style would eventually turn off voters. Much of the Republican rank-and-file judges him a strong leader and backs his proposal to bar Muslims from entering the United States.

Marco Rubio hopes to profit from his willingness to support government surveillance programs that his rivals Ted Cruz and Rand Paul have opposed. Cruz casts himself as an “America first” leader who, unlike Rubio, won’t repeat Bush’s mistakes in Iraq even as he vows to “carpet-bomb” the Islamic State.

Under once-conventional political calculations — discounting both her gender and party affiliation — a shift toward national security would put Hillary Clinton at a disadvantage next November. The Democratic incumbent she aims to succeed is already on the defensive.

Yet Clinton has managed to etch a slightly more hawkish profile than President Barack Obama. And her first-term service as his secretary of state gives her more national security experience than any other major candidate, although whether that will pay off is unclear.

“Lack of experience may be better than the experience she does have,” cautioned Jan van Lohuizen, Bush’s pollster in 2004.

That’s one big question for the campaign’s new contours. Even bigger is whether the shift will last.

“I don’t know how durable this is,” van Lohuizen said. “Eleven months is a long way to go.”

© 2015 The New York Times Company