A French victory at Trafalgar was only the first hurdle

What follows if the Franco-Spanish fleet wins at Trafalgar?

It earns the right to fight several successively larger Royal Navy forces before any invasion crossing becomes possible.

A Franco-Spanish victory over Nelson would leave the surviving ships facing further British forces. The proposed sequence begins with the Western Squadron and continues to the Channel force under St Vincent. The Chatham and North Sea squadrons could then combine as another barrier. In this counterfactual, each successive opponent is described as larger. Winning at Trafalgar would therefore leave further fleet actions before a crossing with an invasion army became possible.