Terrorism typically ratchets up nationalistic impulses in presidential campaigns, a Stanford sociologist says.

But which candidate benefits from this dynamic is more nuanced than most political observers realize, said Robb Willer, a Stanford professor of sociology. Stanford News Service interviewed him recently about how terrorism may impact the 2016 presidential campaign, which has all challengers and no incumbent vying for the nation's top office.

What does research say about how the war on terror will influence presidential elections?

Probably the most reliable finding from research on the political impact of terrorism is that the threat of terrorism increases support for standing leaders. This is one example of a larger dynamic called the rally-around-the-flag effect, or simply, rally effect. A rally effect occurs when war, terrorism or some other security threat leads citizens to support incumbent leaders more. For example, I found in this study that between 2001 and 2004 governmental announcements of terror threats to the U.S. tended to lead to significant increases in President George W. Bush's approval rating. The support Bush derived from the threat of terror and his policy responses to it likely played a key role in his reelection in 2004.

The takeaway for incumbents is that their support will go up – potentially to a tremendous extent – following terror threats if their policies on terrorism are viewed positively or at least neutrally. But they also risk losing support if their policies are viewed negatively. For example, support for President Jimmy Carter initially rose following the 1979 attack on the U.S. embassy in Iran, but subsequently fell as his handling of the hostage crisis came to be viewed negatively, finally contributing to his loss to Ronald Reagan in the 1980 presidential election. Generally, incumbents get the benefit of the doubt following security events, but they risk big losses if they are seen as ineffective in fighting the threat.

In your opinion, how might the ISIS threat play out in this year's presidential election?

My own take is that terror threats have two main psychological effects. First, they sharpen national boundaries and increase nationalist spirit. This drives the rally-around-the-flag effect. In the context of an election, this means that the candidates who will derive the most increased support from such threats are those seen as unambiguously patriotic, who support national symbols and who support maintaining and/or restoring America's global standing.

Secondly, terror threats increase fundamental security concerns. This leads to greater support for leaders who are seen as most able and motivated to defend the nation. So, candidates who are perceived to be associated with strong foreign policy, who support the military and who take positions seen as likely to reduce the threat will be supported more. Candidates who are not as clearly pro-military, who do not project a strong and powerful persona or who are seen as backing policies that could compromise national security risk losing favor in such periods.

But in understanding the impact of terror threats on the 2016 election, we are to a great extent in uncharted territory. Most past research has focused on views of incumbents. And there is good reason to think that whatever advantage an incumbent experiences does not necessarily transfer to candidates of the same party. For example, we found in a large-scale experiment in 2008 that presenting Americans with a news report about the threat of terrorism led to decreased support for Sen. John McCain among political moderates. The support Bush derived from terrorism in 2004 did not extend to McCain in 2008, though this may have been in part because the conservative-led Iraq War had become very unpopular by 2008.

Does the specter of terrorism favor conservative or liberal politicians in the minds of those polled?

In general, the specter of terrorism benefits conservative more than liberal politicians. Conservative positions on a variety of issues, including national defense, military funding and immigration, are more popular during periods of heightened terror threat. Further, conservative politicians are more likely to support militant foreign policy positions than liberals, while liberals are more likely to support diplomatic solutions. These policy orientations lead conservatives to gain increased support during times of heightened security concern.

That said, if Hillary Clinton wins the Democratic nomination, the effects of the threat of terrorism in the 2016 general election could be more complex. Clinton's extensive State Department experience and facility with foreign policy could neutralize a conservative advantage on terror policy. The result could be that the effects of the terror threats on the 2016 general election are a wash.

The threat of terrorism could conceivably have its greatest electoral impact on the 2016 Democratic primaries, where Clinton could pull support from Bernie Sanders as a result of the issue's prominence. However, it is also the case that Democratic voters tend to report lower concern about terrorism than either Republican or Independent voters, so it might require further escalation of the threat of terrorism in the U.S. for Clinton to gain support from the issue.

Is terrorism more important than the economy to voters?

Overall, it is not. Many more elections are determined by perceptions of candidates' economic policies than their anti-terror policies. However, when terror threats are especially strong, they can be as impactful as any issue, even more impactful than the economy. Terrorism is the sort of issue that can have an outsized impact because it taps into our most fundamental fears and concerns. Support for President George W. Bush's handling of the economy increased 18 percent following the 9/11 attacks. This is an astonishing figure considering that Bush was, appropriately, focused almost entirely on non-economic issues following the attacks, but one which shows how much more important terrorism can be following threats; it has the power to even shape views of economic policy.

It is impossible to say at this time which of these issues will be more prominent in the 2016 election, but history would suggest we should bet on the economy.

How could the threat of terrorism affect Donald Trump's presidential candidacy?

The rise of the terrorism issue has potentially powerful implications for Trump's candidacy. As recently as last month, many analysts suggested we had already witnessed "peak Trump" – that his candidacy couldn't gain greater support because of the outrageousness and xenophobia of his rhetoric. But this may have underestimated the potential for an issue like terrorism to increase the viability of a candidate like Trump who is associated with patriotism, militant foreign policy and opposition to immigration, all positions that are favored more following terror threats.

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