“The principal objection would be: Does such a move actually contribute to the stability in Europe, or would it contribute to destabilization?” said Douglas E. Lute, a former U.S. ambassador to NATO. “I think it’s indisputable there wouldn’t be consensus among the 30 members, even though all allies agree that Ukraine has the right to aspire to become a NATO member.”
Stephen M. Walt, a professor of international affairs at the Harvard Kennedy School of Government, said that even in the 1990s, when NATO enlargement was first proposed, many prominent American strategists opposed it for this reason. “That was the concern all along — it wouldn’t be easy to do this in a way that wouldn’t threaten Russia,” he said.
Ukrainian leaders have waffled on NATO membership.
Ukrainian leaders have not always pushed hard to join NATO, and that has shaped the American approach.
Former President Viktor Yushchenko wanted entry into the alliance, but Ukrainians became more reluctant after Russia invaded Georgia. His successor, Viktor Yanukovych, dropped any drive for membership and promoted closer ties with Russia, even agreeing to allow Moscow to continue leasing a Black Sea naval port in Crimea.
During the Obama administration, American officials encouraged Ukraine to sign a formal association agreement with the European Union rather than to try to join NATO. Mr. Putin pressured Mr. Yanukovych to reject the agreement, which led to the Euromaidan protests in 2013 that eventually ousted Mr. Yanukovych.
“A lot of the U.S. policy has been quite reactive due to circumstances,” said Fiona Hill, a Russia expert at the Brookings Institution who was a senior director for Europe and Russia on the National Security Council under President Donald J. Trump. “It has also changed due to changes in Ukraine itself toward this.”
“By now, you’ve got much more sentiment in Ukraine for joining NATO,” she added.
Mr. Zelensky has pressed Mr. Biden repeatedly on membership, including during his visit to the White House in September. “I would like to discuss with President Biden here his vision, his government’s vision of Ukraine’s chances to join NATO and the time frame for this accession, if it is possible,” he said as he sat next to Mr. Biden.