Is the NATO doctrine still considering a retreat from the national borders with Russia and a defense in depth, in wake of an American mass troop deploying in Eastern Europe?

The NATO doctrine does not explicitly state a retreat from national borders with Russia or a defense in depth as a general strategy. However, the recent military exercises and deployments suggest a focus on strengthening the alliance's defense capabilities and deterrence posture in the face of potential threats from Russia.

1. Steadfast Defender 2024: The largest military exercise since the Cold War, known as Steadfast Defender 2024, involves around 90,000 troops from NATO allies and Sweden. This exercise is designed to rehearse how U.S. troops could reinforce European allies in countries bordering Russia and on the alliance's eastern flank. The exercise aims to demonstrate NATO's ability to reinforce the Euro-Atlantic area with a transatlantic movement of forces from North America.
2. Doctrine and Military Presence: NATO's military presence in the eastern part of the alliance territory is an important component of its deterrence and defense posture. This presence is likely to be reinforced by the ongoing military exercises, which are part of a broader strategy to enhance the alliance's collective defense capabilities.
3. Recent Developments: The recent developments, including large-scale military exercises and troop deployments, suggest a proactive approach by NATO to strengthen its defense and deterrence capabilities in the face of potential threats from Russia.

In conclusion, while the NATO doctrine does not explicitly state a retreat from national borders with Russia or a defense in depth, the current military exercises and deployments indicate a strategy that focuses on reinforcing the alliance's defense and deterrence posture along the eastern flank, in response to the geopolitical situation with Russia.