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[^8]. 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[^10]. The exercise aims to demonstrate NATO's ability to reinforce the Euro-Atlantic area with a transatlantic movement of forces from North America[^8].
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[^4]. 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[^2][^3].
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[^7][^9][^10][^11].

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.