During the first debate among Democratic primary candidates Wednesday evening, the assembled presidential hopefuls were asked a simple question: What is the greatest geopolitical threat to the United States?

The 10 candidates gave different answers, and Washington Gov. Jay Inslee suggested that President Trump himself was the greatest threat to America, while Sen. Amy Klobuchar (Minn.), singled out the situation with Iran in the Middle East.

But otherwise, there were some fairly consistent themes. China was named by four candidates, while both climate change and the threats posed by nuclear weapons were named by three candidates.

“China, without a question. They are wiping us [out] economically,” said Rep. Tim Ryan (Ohio).

Not mentioned in the list of greatest threats, and barely mentioned at all during the debate in general, was terrorism and the subsequent war on terror that has helped to define almost two decades of U.S. foreign policy.

The most notable reference to terrorism in the debate was arguably an error — when Ryan suggested that the Afghan Taliban “started flying planes into our buildings.” The remark prompted boos from the audience in Miami.

“The Taliban didn’t attack us on 9/11,” Rep. Tulsi Gabbard (Hawaii) interjected. “Al-Qaeda did.”

This may be an important shift in the electoral debate about U.S. foreign policy. In the first debate among Republican candidates ahead of the 2016 election, held in August 2015, terrorism dominated much of the discussion of the threat posed to the United States, with many of the candidates talking about the Islamic State.

During a later Republican debate in 2015, the word “terror” was mentioned a whopping 81 times by the candidates and the moderators. In contrast, that same word was mentioned three times Wednesday evening.

It is possible that the 2020 candidates featured Wednesday will discuss their thoughts on the threats posed by terrorism in greater depth in later debates or that candidates who will debate Thursday will focus on terrorism more greatly.

It may also be a reflection of the different priorities of Republican and Democratic voters.

In a Monmouth University poll released December 2015, shortly after the Republican debate, 46 percent of Democratic voters ranked jobs and security as their top priority, compared with 36 percent who listed national security and terrorism. In contrast, 57 percent of Republicans said national security was a top issue, compared with 41 percent who named jobs and the economy.

But if the lack of discussion of terrorism this week continues, it may be a reflection of the shifting ideas of what poses a threat to the United States. The 2015 debates took place ahead of a sudden spate of high-profile terrorist attacks in Western Europe, many orchestrated by groups with links to the Islamic State.

These attacks undoubtedly changed the tenor of the 2016 presidential debate — even among Democrats. While the first Democratic candidate debate in October 2015 only mentioned terrorism briefly, a huge Islamic State-orchestrated attack in Paris the following month forced the candidates to talk in depth about extremism during their next debate.

“Together, leading the world, this country will rid our planet of this barbarous organization called ISIS,” Sen. Bernie Sanders (I-Vt.) said, using an acronym to describe the Islamic State.

The attacks in Paris and elsewhere helped focus the foreign policy section of the 2016 debate around terrorism. A Pew poll from July 2016 found that voters thought that terrorism should get more time than any other subject in presidential debates between the two final candidates, Trump and Hillary Clinton.

For Trump, who tweeted frequently about terrorism but had never held elected office nor a government position, the subject matter may have been an advantage. Nate Silver, a polling expert with the website FiveThirtyEight suggested in March 2016 that Trump’s tweeting after terrorist attacks helped him capitalize on anti-Muslim sentiment during the campaign.

Trump has spoken about terrorism less frequently since taking office, however, perhaps a reflection of the military defeat of the Islamic State in Syria and Iraq and data that shows that terrorism attacks have declined since 2017.

In January 2018, Trump’s then-Defense Secretary Jim Mattis unveiled a strategy that placed less emphasis on terrorism and more on the threat posed by great powers such as China. Mattis resigned from his position in December 2018 as a rebuke over troop withdrawal from Syria.

In some ways, a shift to focusing on the threat posed by China rather than that posed by terrorism would be a reversion to a norm. Even in 2007, candidates were already stating that there had been too much of an emphasis on the latter over the former.

“I think that what’s happened with the last seven years of the Bush administration is America’s faced, over the long term, with two very serious challenges, one of which they’ve been obsessed with, which is the issue of terrorism,” John Edwards (D), a former senator from North Carolina, said in 2007.

“The other is the rise and strength of China, which they’ve done virtually nothing about,” Edwards said.