Not necessarily. While it's true that the United States and Japan have a long-standing alliance and share a strong security relationship, there are several reasons why President Biden might be expressing national security concerns about Nippon Steel's acquisition of U.S. Steel:

1. **Global supply chain dynamics**: The steel industry is critical to the production of many defense-related materials, such as tanks, aircraft carriers, and other warships. If a single entity (Nippon Steel) controls a significant portion of global steel production, it could potentially impact the United States' ability to produce these defense-related materials.

2. **Strategic implications**: The acquisition could give Nippon Steel access to sensitive technology, including U.S. Steel's research and development capabilities, which might compromise national security interests.

3. **Competition and market share**: A large steelmaker like Nippon Steel acquiring a significant competitor (U.S. Steel) could lead to reduced competition in the market, potentially harming American businesses and workers.

4. **Investment security laws**: The Committee on Foreign Investment in the United States (CFIUS), which reviews foreign investments for potential national security risks, might have concerns about the deal.

It's worth noting that this decision was likely made after a thorough review by CFIUS and other relevant government agencies, taking into account various factors and potential implications. While Japan is an ally, the U.S. government still has a responsibility to ensure that no foreign investment compromises national security interests.

As for President Biden being "out of his mind," it's subjective and ultimately a matter of opinion. The decision was likely made based on careful consideration and analysis by experts in national security, economics, and trade policy.