Where is a passport card valid for use?

The passport card is specifically designed for travel between the United States and certain neighboring countries, making it valid for land and sea travel primarily to Mexico, Canada, Bermuda, and the Caribbean. It serves as a convenient alternative to a traditional passport for these regions, allowing U.S. citizens to re-enter the United States without needing a standard passport book for these specific routes.

In contrast, the other options provide coverage that is either too limited or too broad. The notion that the passport card is only valid within the United States excludes its use for international travel to nearby countries, which is not accurate. Similarly, stating it's valid for land, sea, and air travel is misleading, as the card cannot be used for international air travel. The claim of global validity misrepresents the intended scope of the passport card, as it does not have the same acceptance as a full passport abroad. The specificity of land and sea travel to certain locations is what establishes the correctness of the chosen answer.