Donald Trump’s announcement that he intends to withdraw the US from the Paris climate agreement has sparked renewed interest in the question of what the agreement actually requires countries to do.

Trump himself was characteristically incoherent in his announcement, calling the agreement both “non binding” and “draconian” in the same sentence. The recent G20 communique also studiously avoided this question. While the communique’s unprecedented split language on climate change noted Trump’s decision to cease implementation and eventually withdraw from the agreement, it did not comment on the legal implications of that decision.

Most legal analysts, climate negotiators, and other close observers of the process have taken the position that the agreement itself makes emission reduction pledges essentially voluntary, since countries have free rein to set their own targets and policies and are not required to meet the targets they put forward.

Although these commentators are mainly correct, the truth is that whether or not the pledges are legally binding is not that important to the effectiveness of the agreement. What really matters is whether countries are willing to hold each other accountable for putting forward ambitious pledges and making good faith efforts to meet them.

Under the agreement, countries are expected to put forward their own “nationally determined” contributions and periodically report on their progress toward meeting them. Since the pledges are self-defined and non-binding, peer pressure, not legal obligation, must do the hard work of driving ambition, deterring free-riding and ensuring accountability.

For this to work, countries must actually be willing to press laggards to take actions that are consistent with the overarching goals of the agreement. If it becomes evident that there are no consequences for shirking responsibility, even the most rigorous reporting and review will not be sufficient to ensure that countries do their share or honour their pledges.

While all this has been clear from the start, the Paris Agreement is rarely described as politically enforceable. That may be partly due to the fact that the concept of political enforceability has a rather checkered history in climate diplomacy.

After the 2009 Copenhagen climate conference spectacularly failed to secure a legally binding agreement, some parties (including the US) sought to put a brave face on the outcome by insisting that the Copenhagen Accord was “politically binding” because of the hands-on involvement of heads of state in negotiating it. Many participants and observers balked at this effort to salvage a deeply disappointing outcome and dismissed the notion of a politically binding agreement as a pale imitation of the legally binding treaty they were looking for.

Much of the objection to the concept of “political bindingness” stems from the inclination to conflate an agreement’s legal character with its enforceability. Many believe that a legally binding agreement is, by definition, more enforceable than a politically binding one.

But this need not be the case. For example, the United Nations Framework Convention on Climate Change (UNFCCC) is a legally binding treaty, but as its name implies, was only intended to be a broad “framework” for elaborating more specific pledges in future agreements (like the Kyoto Protocol and Paris Agreement). For that reason, it included only vague commitments and has a dispute resolution mechanism that is consent-based and non-binding.

By contrast, the Iran nuclear deal is readily enforceable even though it is not legally binding. It contains very detailed requirements for Iran to curtail its ability to process nuclear material in exchange for specific, stepwise relief from economically debilitating sanctions by the P5+1 countries (the United Kingdom, France, China, Russia, the United States, Germany and the European Union). Thus, it is politically enforceable in that each side could be subjected to rather serious consequences in the event of a breach. US secretary of defence James Mattis, a harsh critic of the Iran deal, recently conceded its politically binding nature when he told the New Yorker that “I would not have signed the Iran deal, but it’s signed – we gave our word and we have to play the ball as it lies.”

What the comparison between, for example, the original UNFCCC treaty and the Iran deal shows us is that the perceived interests of the parties, more than the legal form of the agreement, determines the strength of the enforcement regime and the incentives for compliance.

In the Iran deal, the P5+1 were convinced that their core national interests would be put at risk by a nuclear armed Iran, and they were willing to deploy substantial economic and diplomatic resources to avert that threat. On the other hand, in 1992, the parties to the UNFCCC did not yet fully perceive climate change to present the same kind of imminent risk to vital interests that is now widely recognised and therefore accepted weaker incentives for action and compliance.

All of which is to say that, like the Iran deal, the Paris Agreement is, at the end of the day, a political agreement. Its success will depend on the extent to which countries have come to see climate change as a threat to core interests and are therefore willing to enforce it.

Rehabilitating the concept of political enforceability in climate diplomacy could help in this regard. The Agreement would be better positioned to withstand Trump’s stated intent to cease implementation and eventually withdraw if its strongest champions talked openly about parties being politically bound to their pledges and about the political consequences of failing to adhere to them. Whereas in Copenhagen this might have been seen as an admission of weakness and defeat, in today’s context it should be understood as showing strength and resolve.

Steve Herz is a senior attorney with the Sierra Club’s International Climate Programme

[This article originally appeared on climatechangenews.com]