Ukraine is seeking commitments from NATO at upcoming Vilnius summit. Are allies willing to give them?

As world leaders prepare to gather this week for a much-anticipated NATO summit in Vilnius, Lithuania, the alliance's unity may be newly tested as divisions over the type of assurances made to Ukraine regarding its future membership become starker. 

More than 500 days into a grinding war launched by Russia in February 2021, Ukraine has pressed for a detailed path toward membership into the alliance that some member countries appear reluctant to provide.

The impasse has prompted concerns in Kyiv and among some eastern European NATO members that the Vilnius summit – touted for weeks by the Biden administration as a show of enduring support – may result again in ambiguous commitments reminiscent of those made in Bucharest in 2008.