Moldova, which is also an official candidate for EU membership, is paired with Kyiv in the accession process and cannot move ahead as long as the impasse persists.

Under Costa’s proposal, so-called negotiating clusters — key legal steps on the path to membership — could be opened with the assent of a qualified majority of EU countries rather than unanimous agreement. Closing a cluster would still require the support of all the EU capitals, but the lower standard for opening negotiations would allow Ukraine and Moldova to begin the reforms necessary to demonstrate progress toward EU standards in particular policy areas. They could move their membership bids forward even if one or two countries are opposed, according to a person familiar with the plan.

According to the diplomats, Costa has been lobbying EU leaders directly during a recent “tour des capitales” where he met with several European leaders, as well as during bilateral talks on the sidelines of the United Nations General Assembly last week in New York.

“Enlargement is an important priority for the president of the European Council,” said one of the officials. “He sees it as the most important geopolitical investment the EU can make. That’s why he believes it is important to continue discussing avenues to ensure that Ukraine’s reform efforts can be translated into tangible steps.”

Marta Kos, the EU’s enlargement commissioner, will head to Ukraine on Monday as the country completes the screening process of the  legislation required to move ahead with its candidacy.

“All clusters have been screened, in record time. Ukraine has delivered. Ukraine is ready for the next step. It’s now up to member states to give the green light,” Kos told POLITICO’s Brussels Playbook. “Both Ukraine and Europe cannot afford to see Ukraine’s momentum for reforms slow down. This is the moment to accelerate.”