Biden administration officials now privately concede there is no evidence that conclusively points to Moscow’s involvement. But publicly they have deflected questions about who might be responsible. European officials in several countries have quietly suggested that Ukraine was behind the attack but have resisted publicly saying so over fears that blaming Kyiv could fracture the alliance against Russia. At gatherings of European and NATO policymakers, officials have settled into a rhythm; as one senior European diplomat said recently, “Don’t talk about Nord Stream.”