Big cities in France never vote far-right, and the PS (left) candidate is leading the polls in Paris' next election, so I'm really not sure what you're talking about. Gentrification is hardly a cause for far-right coming to power.
The idea that Paris is more dangerous than any big city in the US is laughable, and any person that thinks otherwise or that believes anything that Trump spouts is either gravely uneducated at best, or an absolute moron at worst.