Poli-Sci Perspective is a weekly Wonkblog feature in which Georgetown University's Dan Hopkins and George Washington University's Danny Hayes and John Sides offer an empirical perspective on the issues dominating Washington. In this edition, Hayes looks at the way foreign leaders can influence America's foreign policy. For past posts in the series, head here.

When the United States is considering entering into war, sometimes the most important voices can come from other countries.

Recent research raises the intriguing possibility that Americans’ views about U.S. foreign policy can be influenced not just by the president and members of Congress – the elites from whom the public typically takes its cues – but also by the leaders of other nations and the United Nations.

That might sound bizarre. Would Americans, often portrayed as parochial and insular (freedom fries, people), really take direction about U.S. foreign policy from the accented pronouncements of foreigners? Mon dieu!

But my new book with Matt Guardino, Influence from Abroad: Foreign Voices, the Media, and U.S. Public Opinion, says yes. Under some circumstances, international actors can influence whether Americans support U.S. military interventions.

Guardino and I studied the lead-up to the 2003 Iraq War. In the days before the United States lit up the Baghdad night with its “shock and awe” campaign, public opinion was starkly polarized. Just a week before the invasion, upwards of 90 percent of Republicans favored military action, but just 44 percent of Democrats did, according to one Pew survey.

That kind of wide partisan gap typically opens only when the leaders of the Republican and Democratic parties take diverging positions on an issue, which makes the polarization before the Iraq War a curious puzzle.

While Republican elites, rallying behind the Bush administration’s push for action, were full-throated in their support for an invasion, Democratic elite opposition was muted. Even a majority of Democratic senators – including the 2004 presidential ticket of John Kerry and John Edwards and the near-nominee in 2008, Hillary Clinton – voted for the congressional resolution that authorized Bush to use force against Saddam Hussein.

Of course, some liberal Democrats, such as the late-Sen. Robert Byrd (W.Va.), were vociferous in their opposition. “This is no small conflagration that we contemplate,” Byrd said on the Senate floor in February 2003. “It is not going to be a video game.

But the public hardly heard any of it.

In our analysis of every nightly network television story about Iraq in the eight months before the war – 1,434 stories in all – Guardino and I found that Democrats accounted for just 4 percent of all statements in the news. Other domestic sources who opposed the war, such as protesters and anti-war groups, made up an even tinier fraction. By contrast, Bush administration officials arguing for military action constituted 28 percent of all statements in the news. When we looked at national newspaper coverage, we found the same thing.

Yet many Democrats in the public, and about one-third of independents, remained opposed to the war, even without clear opposition signals from domestic elites. Why did that happen?

Although the U.S. media paid little attention to dissent from domestic voices, Guardino and I found that they devoted significant air time to opposition to the war from overseas. (In the book, we discuss at length why journalists largely ignored opposition from congressional Democrats and anti-war groups.)

In our analysis of network news coverage, foreigners were the sources of 34 percent of all statements that appeared on the air, and 65 percent of all of the anti-war statements. The most common sources were U.N. weapons inspector Hans Blix and U.N. Secretary-General Kofi Annan, numerous anti-war members of the British parliament, and various officials from France, Germany and other European governments. When Americans heard opposition to the war, those objections came from abroad.

In turn, the coverage of overseas opposition suppressed public support for the Iraq invasion. According to our analysis of a series of pre-war opinion polls, support for the invasion was about nine percentage points lower than it would have been without foreign opposition in the news.

Certain people were especially responsive. College-educated Democrats were 37 percentage points less likely to support the war because of opposition from overseas. Independents with college degrees were 59 percentage points less likely to advocate invasion than they would have been in the absence of foreign dissent. Republicans, not surprisingly, were unmoved.

The effects were strongest among these groups for two reasons. First, highly educated people pay more attention to the news and so were more likely to be exposed to the reported opposition. Second, Democrats and independents are far more likely than Republicans to be skeptical of pre-emptive military action and to have favorable attitudes toward European governments and the United Nations. As a result, they were much more responsive to these foreign voices.

Of course, foreign-induced opposition didn’t stop the invasion. Public opinion is but one consideration for political leaders. But it did mean that President Bush took the country to war with a polity far more divided than it would have been otherwise. This left him with a weaker base of support to draw on as the conflict ground on, hastening the slide in his approval ratings and accelerating dissatisfaction with the war.

Guardino and I aren’t the only researchers to find that citizens may look overseas for guidance about U.S. foreign policy. One paper suggests that Americans, and especially those who don’t trust the sitting president, look to the United Nations for a “second opinion” about whether to support military action. The boost in presidential approval at the outset of a military conflict – the “rally round the flag” effect – is significantly larger when the United Nations endorses the action than when it does not. Views about whether the United States should attack Iranian nuclear facilities might also depend on U.N. support.

The debate over the Syrian conflict is, of course, very different from the Iraq War (or the debate over Iran’s nuclear program, for that matter). But recent news coverage has already highlighted the relevance of various international actors, from the United Nations to Israel to Turkey and more.

It remains to be seen whether these voices will shape Americans’ attitudes as they contemplate another conflict in a far-off land. But it certainly seems prudent for the Obama administration to try to cultivate support for its Syria policy not only on Capitol Hill, but around the globe.