Did Mahan help turn the Panama Canal into policy?

Without Mahan, might the Panama Canal have remained only a failed aspiration?

Possibly. Mahan, Roosevelt, and others helped make the political and strategic case for building it.

Mahan, Theodore Roosevelt, and other advocates helped make the case for constructing a canal. Whether the project would have failed without Mahan remains uncertain, so his importance as an advocate does not establish that construction depended on him alone.