'In 2006, President Victor Yushchenko attached high priority to securing a NATO membership action plan (MAP). By summer, Kyiv looked on course to attain a MAP when alliance foreign ministers met that December. Curiously, Moscow did not come out hard against the idea. The prospective MAP derailed, however, after Yushchenko appointed Victor Yanukovych as prime minister. During a September visit to Brussels, Yanukovych said he did not want a MAP. The proposal died given the divided position of Ukraine’s executive branch.

Yushchenko called for a MAP again in January 2008, this time with the support of Prime Minister Yuliya Tymoshenko and Rada (parliament) Speaker Arseniy Yatseniuk. Moscow came out in full opposition. When Yushchenko visited the Russian capital that February, he had to stand alongside and listen to President Vladimir Putin threaten to target nuclear missiles on Ukraine. Instead of lobbying allies to support a MAP for Kyiv, Washington waited until the April Bucharest summit, where President George W. Bush attempted to persuade his counterparts to grant Ukraine (and Georgia) a MAP. However, a number of allied leaders by then had made up their minds and opposed the idea. Concern about Russian opposition undoubtedly played a role.'
https://www.brookings.edu/blog/order-from-chaos/2019/06/06/natos-ukraine-challenge/