It wasn't 'semi-finished'.
The French had excavated some 30,000,000 cu yd in a futile effort to build a fantasy sea level canal in the 13 years they worked there. The US excavated some 170,000,000 cu yards in 10 years PLUS put into place the entire lock system and the massive Gatun dam (largest in the world at the time) and Gatun lake, which was the largest artificial lake in the world. Not to mention other innovations like figuring out how to control diseases like malaria and yellow fever in the region.
The idea that the French did anything worthwhile at the Panama Canal is preposterous and completely counter to the actual facts.