For decades, Republicans have been more supportive than Democrats of an interventionist foreign policy. Surveys conducted earlier this year showed that Republicans were consistently more likely than Democrats to support striking Syria if Assad used chemical weapons. But partisanship is powerful in the age of President Obama, powerful enough to overcome longstanding partisan preferences on international affairs. A new poll shows that the president can’t count on the traditional coalition for the use of force abroad.

This morning, NBC News released a survey showing that only 42 percent supported striking Syria, with 50 percent opposed. Those numbers flip when the question specified that the US would rely on airstrikes and stand-off range weapons, like cruise missiles. Then, 50 percent were on board. That probably means the president doesn’t have to worry too much about public support in determining whether and how to strike Syria.

But even narrow support for strikes is underwhelming compared to earlier surveys from Quinnipiac, CNN, Pew, and The Washington Post, which asked voters hypotheticals about how they would react to a Syrian chemical weapons attack. Those polls suggested that a majority or plurality of voters would support strikes.

So what’s the difference between those earlier surveys and today’s NBC poll? Republicans. In every previous survey, Republicans were most likely to support attacking Syria. Each poll showed more than 50 percent of Republicans willing to strike Assad if he used chemical weapons. Today’s NBC News poll shows far less Republican support, with just 41 percent in support and 49 percent opposed. That’s 15 points less than April’s Pew Research survey, which found that 56 percent of Republicans would support strikes. In comparison, Democratic support hasn’t declined—46 percent support strikes, just like in April. And so for the first time, more Democrats support intervention than Republicans.

The easiest explanation is partisanship. The president has clearly signaled his intention to strike Syria, Republican leaders have sent mixed signals, and the party rank-and-file has taken the cue. That’s not overly surprising and largely consistent with research by political scientists, although perhaps the extent of the drop should be a bit surprising, given the party’s relatively recent willingness to bomb every country between the Mediterranean and the Karakoram, at one point or another.