If I asked you whether Americans were more likely to name immigrants and refugees a critical threat to the United States in 1998 or in 2016, which year would you guess? Most people, I think, would quickly choose 2016. Most people, however, would be wrong.

According to the Chicago Council on Global Affairs, in 1998 53% of Americans did so, compared to 43% in 2016. The error would be understandable, of course, given the homegrown terrorist attacks in Europe and the U.S. over the past year, Trump’s tough talk about Muslim immigrants, and the vigorous debate about Syrian refugees. Indeed, at first glance the numbers are puzzling.

When we break down the responses by political affiliation, however, we get our first clue about what is going on. As it turns out, in 1998 Republicans and Democrats were closely aligned in their assessments – 56% of Republicans and 58% of Democrats saw refugees and immigrants as a critical threat, a difference smaller than the margin of error in the survey. But by 2016 67% of Republicans did so compared to just 27% of Democrats.

The next piece of the puzzle is the timing of several major shifts in opinion. Republican and Democratic opinions remained closely aligned in 2002, with 62% of Republicans and 58% of Democrats naming refugees and immigrants as a critical threat. The first significant partisan gap emerged in 2004. At that point 62% of Republicans still identified refugees and immigrants as a critical threat but only 49% of Democrats did so. The second pivot point was 2010, when Democrats threat assessments began a steady drop: down to 41% in 2010, 30% in 2012, and just 21% in 2014. Over the same period Republican concerns waned somewhat as well, dropping from 62% to 55%. From 2014 to 2016 Republican concerns ramped sharply upward, to 67%, while Democrats grew somewhat more concerned, with 27% identifying refugees and immigrants as a critical threat.

The timing of these shifts in opinion is not coincidental. These threat perceptions reflect the fact that American foreign policy has become increasingly polarized since September 11, 2001. The emergence of the partisan gap on refugees and immigrants in 2004 followed the invasion of Iraq. The second shift appeared in 2010 in the first poll taken after the election of Barack Obama. Neither of these events, of course, have anything to do with the threat posed by refugees and immigrants. They both, however, produced massive levels of partisan rancor. By mid-2004, nearly 80% of Republicans still supported the war, but roughly 80% of Democrats opposed the war. Returning the favor, Republicans have blasted Obama’s approach to foreign policy at every turn. Republicans have blamed Obama for losing Iraq, for not standing up to China and Russia, and more generally for a failure of leadership on issues from the Syrian civil war to ISIS.

Since 9/11, in short, when pollsters call Americans to ask them how they feel about refugees and immigrants, their responses increasingly reflect the widening gap between Democrats and Republicans rather than a cold-eyed assessment of the actual threat they perceive.

Nor is this an isolated case. The same pattern can be seen if we look at how Americans assess the threat of Islamic fundamentalism. As the same Chicago Council report reveals, in 1998 there was a ten-point gap between parties, with 42% of Republicans and 32% of Democrats identifying it as a critical threat. After 9/11 those figures jumped to 70% for Republicans and 59% for Democrats. By 2016, however, the partisan gap had grown to 30 points, with just 49% of Democrats calling Islamic fundamentalism a critical threat to the United States compared to 75% of Republicans.

The upshot is that the next president, whether Trump or Clinton, will not be able to rely on the public for stable, majority support for foreign policy. Though Americans will coalesce around direct threats to the homeland, partisan lenses color their views of the rest of the world. There are few issues from immigration to intervention that will not quickly become polarized. Given that the platforms of both candidates have already engendered so much debate, the next four years of foreign policy promise to be heavily contested on all sides.