It must first be noted that Turkey, Greece, and the EU have failed on humanitarian grounds with the way they've approached the problem over the last few months.

Turkey tried to funnel migrants from different countries to Greece in order extract concessions from the EU. Greece pushed back the migrants using methods that are totally unacceptable from a human rights perspective. The EU practically endorsed Greece's breach of human rights and European values by extending unconditional support to it despite the actions of the Greek security forces at the border and in the Aegean Sea.

The EU and Turkey should focus their efforts on renewing their cooperation, and the 2016 EU-Turkey Statement and Action Plan is a good, if imperfect, starting point.

The plan is based on a tripartite mechanism through which Turkey takes any necessary measures to prevent irregular migration to Europe. All new irregular migrants crossing from Turkey to the Greek islands are returned to Turkey, and for every Syrian being returned to Turkey from the Greek islands another is resettled in the EU. This mechanism proved to be effective soon after the action plan was agreed. According to theEuropean Commission, "Three years later, irregular arrivals remain 97% lower than the period before the statement became operational, while the number of lives lost at sea has decreased substantially."

Spanner in the works

What has not worked is the incentive structure for Turkey. Initially, the EU allocated €3 billion ($3.27 billion) under the Facility for Refugees in Turkey and mobilized up to an additional €3 billion by the end of 2018. This has been largely, if not entirely fulfilled. And as long as that remains the case, the EU won't commit new funds beyond those announced for up to 2018.

According to the agreement, the EU and Turkey committed to improve humanitarian conditions inside Syria, but nothing happened in this regard. The EU has been and remains highly critical of Turkey's military incursions into Syria.

Arguably, the financial issues are easier to settle. The agreement also includes incentives for Turkey regarding its EU accession process and other projects toward integration that have nothing to do with the refugee crisis. These incentives include a speedier visa liberalization process and upgrading the Customs Union. However, they were unrealistic in the first place against the backdrop of Turkey's democratic deficits and public opinion  with the EU about Turkey.

Read more: Ankara, Athens exploit refugees in dangerous political game

Don't repeat the mistakes

Turkey thinks that it has kept its side of the bargain, but that the EU has failed to do the same. That prompted President Recep Tayyip  Erdogan to threaten to suspend the agreement and action plan. That in turn didn't go down well among EU member states. But rather than exchange barbed criticism, what the EU and Turkey really need to do is agree on a new plan. One that builds on the 2016 agreement and revises the incentives for Turkey in a way that better reflects the burden it is bearing.

The new plan should also decouple cooperation on the refugee crisis from the accession process — the former is transactional while the latter is normative, and therefore they have very different dynamics. Turkey and the EU should also cooperate to proactively mitigate crises in their neighborhood before they result in mass migration to Turkey and Europe. This would be in line with Ursula von der Leyen's ambition to lead a geopolitical European Commission.

This is an era when nationalism and populism constrain the policy choices of governments, making international cooperation very difficult. Turkey is currently very unpopular in the EU and Turkish citizens are frustrated with the bloc. Refugees are not welcome anywhere in Europe, including in Turkey.

Read more: Opinion: In Greece, refugees are painted as the enemy

However, the EU cannot entirely externalize the refugee problem even if it forgoes its own values; and Turkey cannot deal with the refugee crisis alone. Therefore, whether they like it or not, the two sides are stuck together on this issue.

Özgür Ünlühisarcıklı is the Ankara Office Director of the German Marshall Fund of the United States.