I generally use medium for drafts of my post and then I post it in Steem. But sometime I forget to post on Steem as it requires some copy pasting, some formatting and some cleaning up to do before I can actually post on Steemit.
So I was googling to see if there were any tools that made it easy. There were none that were usable right away but I came across this npm library https://www.npmjs.com/package/medium-to-markdown I quickly gave it a run on https://npm.runkit.com/medium-to-markdown and could verify that it was working without any issues.
But many users will not be comfortable with the interface. Since I was learning REACT I thought of building a very simple Bootstrap UI for the same and learned a couple of things in the process. 
You can give it a try on -
http://steemtools.bitfolio.org/#/tools/import-from-medium
Let me know if it helps you.