Now, exactly 100 years to the day after Wilson’s decision to enter World War I, Trump responded to a Syrian chemical weapons attack against civilians by launching U.S. missiles against a Syrian airfield, despite repeatedly promising to stay out of the conflict.

Mismatches between words and deeds raise concerns about a state’s reputation and credibility in crises. However, we usually think about situations where leaders fail to follow through on threats — think of Barack Obama drawing a “red line” in 2013 over the use of chemical weapons in Syria and then declining to take military action — and whether leaders suffer politically for publicly “backing out” of a conflict.

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But there is a second type of words-deeds mismatch: when leaders “back in” to a conflict — and use force despite earlier promises to avoid it. Our research finds that when leaders do this, they are also likely to lose public support.

Here’s how we did our research

We tested this with a survey experiment fielded to more than 2,000 respondents — a sample of the U.S. population. Building on previous work, we gauged attitudes toward both types of inconsistency between presidential words and deeds by randomly assigning respondents to different scenarios.

So we told about half of the respondents that the U.S. president issued a threat to intervene, while the other half were told the U.S. president promised to stay out of a conflict. For each sample, half were then told that the president ultimately decided to use military force, while the other half were informed the president refrained from sending U.S. troops. We then asked respondents how much they approved or disapproved of the way the president handled the situation.

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The survey design thus allows us to measure the effect on presidential approval of inconsistency between prior promises on subsequent actions for both types of commitments — “backing out” and “backing in.” Previous studies have looked at the more commonly studied concept of “backing out.” Consistency matters: Our survey shows presidents who make a threat and fail to follow through suffer a 22 percent drop in approval.

However, leaders also face the prospect of punishment for the inconsistency of making a promise to stay out, but then turning around and resorting to military force. Presidents who “back in” to a conflict see their approval fall 12 percent compared to if they had simply issued a threat from the start and followed through with military force. It’s a smaller drop in approval, but still a drop.

Will there be fallout for Trump?

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Will Trump’s sudden policy reversal on Syria hurt him politically, either at home or abroad? Despite already low approval numbers, will his support erode even further? Will the response in Syria help give direction to an apparently aimless foreign policy — or signal that Trump is impulsive and erratic?

Domestically, while many are experiencing a “whiplash” from the sudden shift in Trump’s views on the Syrian conflict, the results are already mixed. Several news outlets reported favorably on the attacks, perhaps because “the news media love a show of force.”

Yet many of Trump’s hard-right supporters, who prefer a hands-off policy in Syria, are greatly upset. But other analysts — even those who approved of the strike — have expressed concern about what this sudden policy change suggests about Trump’s decision-making abilities and temperament.

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Internationally, there’s also a mixed reaction to the U.S. missile strike. Regional allies — including Israel, Turkey, and Saudi Arabia — were very supportive, while Russia and Iran, unsurprisingly, were highly critical. U.S. European allies also generally supported the missile strikes against Syria, but some are unsure if this will lead to a consistent policy.

Our work suggests there’s potential fallout for both immediate domestic support and longer-term foreign policy ambitions. Our research shows that the primary reason publics punish leaders for “backing in” to a conflict is because such actions reflect inconsistency between a president’s words and deeds — and diminish the credibility of U.S. commitments. This affects responses to future U.S. threats.

Foreign leaders may begin to question more deeply the U.S. president’s willingness to stand by his statements. This is particularly important in light of a host of sensitive issues looming on the Trump administration’s docket, including getting tough with China on trade, curbing North Korea’s nuclear weapons program and (perhaps) responding to Russia’s annexation of Crimea and continued involvement in eastern Ukraine — not to mention the U.S. calls for greater burden sharing among NATO allies.

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There are mitigating factors

There may be some bright spots for the Trump administration, however. We further find — consistent with previous research — that leaders can mitigate public concerns about inconsistency by citing new information or new intelligence to explain their change in position. The Trump administration has, in fact, cited new intelligence as the reason for the attack, in an attempt to push back on stories that claimed the policy change was largely an emotional response.

And so far, there has been little discernible drop in Trump’s public standing. But given the many statements and articles highlighting his Syrian policy reversal, further U.S. military action in Syria would likely require Trump to provide more justification and be more careful with his words to avoid the label of “flip-flopper.”

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Jack S. Levy is Board of Governors’ professor of political science at Rutgers University.

Michael K. McKoy is assistant professor of political science at Wheaton College.

Paul Poast is assistant professor of political science at the University of Chicago and a research affiliate of the Pearson Institute for the Study of Global Conflicts.