Washington and NATO are on high alert following the buildup of Russian troops on Europe's eastern front. During a phone call between the US and Russian leaders, Joe Biden threatened Moscow with sanctions should it make any military advances towards Ukraine, while Vladimir Putin stuck to his guns, refusing to back down unless NATO signed a written guarantee that Kyiv will never join its ranks. So will the two sides reach a compromise at the upcoming Kremlin-NATO security talks? And what's at stake if they don't?