Reconnaissance flights and more joint exercises in Central Europe serve to reassure NATO members in the region, but critics say the crisis in Ukraine shows the alliance's relations with Russia need a dramatic rethink.
In the midst of the Crimean crisis, US President Barack Obama is set to host Ukraine's new prime minister, Arseniy Yatsenyuk. The meeting, observers say, is a signal that could not be clearer.
Russia is responsible for the protection of all Russians no matter where they live, comes the message from Moscow. That strikes fear into its former Soviet Republics - and reminds them of recent history.