Hey there!

Since you have a Russian MD degree and you wish to practise in USA; you will have to appear for USMLE and qualify that. Your visa can be sponsored, if you have an outstanding score in USMLE or you have a respected recognition from a notable organization or any other exceptional achievement. In this case, you can practise for free in USA. Apart from this, you cannot practise for free in the USA. For more information regarding the USMLE, you are advised to visit the following links:

https://www.usmle.org/

https://www.usmle.org/bulletin/

Hope this helps. All the best!