Dan Drezner lists the conclusions he drew from a recent conference on foreign policy and political campaigns:

Campaigns take foreign policy promises seriously. Precisely because politicians take credibility and reputation seriously, they really, really do not like to go back on their word when it comes to campaign promises. This does not mean it won’t happen, but it was surprising to me how vehement both campaign operatives and scholars were on this point. If at all possible, winning presidential candidates will carry out their promises. It usually fails to happen only when the candidate, after winning, learns about the second- and third-order effects of implementing those promises. So silly, empty pledges like renegotiating NAFTA appear to be the exception and not the rule.

That makes sense, and it lines up with what I’ve said about this in the past. By making a very specific pledge about the action they will take in office, these candidates are not simply pandering to certain constituencies in their party. They are locking themselves into following through on those pledges if they want to be able to count on the ongoing support of those same constituencies later on. Candidates are also unlikely to want to be accused to “breaking” specific pledges they’ve made during the campaign, so with very few exceptions they’re going to make an effort to follow through on them. So while some candidates’ foreign policy statements may commit them to foolish or dangerous actions later on, we shouldn’t assume that they are merely indulging in empty rhetoric.

That doesn’t mean that some candidates don’t sometimes endorse positions during a campaign (especially a primary campaign) that they later abandon. Obviously, some do, and I assume Clinton’s sudden conversion to becoming an opponent of the Trans-Pacific Partnership will prove to be an example of this. Even so, the more often that a candidate pledges to do something or support a specific policy, and the more emphasis that a candidates gives those pledges in speeches and debate answers, the more likely it is that the candidate intends to fulfill that pledge or at least will try to do so.

Another reason to take foreign policy pledges seriously is that the president has significantly greater leeway in conducting foreign policy and faces fewer constraints than he does when trying to push through a domestic legislative agenda. Especially when a pledge concerns something that the president can do without needing Congressional approval, it is safe to assume that this is something that the candidate will try to do. It may blow up in his face or it may run into more opposition at home or overseas than he expects, but he’ll want to be seen as making the effort.

This is why it matters that virtually every Republican candidate has committed to reneging on the nuclear deal, whether it will be on “day one” or not. They aren’t just paying lip service to what a few hard-line donors or activists want to hear. They are expressing their party’s consensus view that the deal should be scrapped, and they are stating their opposition to a signature piece of the outgoing president’s foreign policy agenda. Most of these candidates also emphasize their opposition to the deal when they speak about foreign policy. If there is one foreign policy pledge from the candidates that we can take seriously as a statement of what they intend to try to do in office, it’s this one.