The bridge is "apply to, be accepted at, and graduate from medical school". Offhand, I personally know at least four physicians who were nurses first, and they certainly worked occasional shifts as nurses during med school for extra money, but it's hard to describe just how big of a torrent of information medical students are expected to absorb. There's very little overlap in the education, although former nurses usually have better simple-procedure skills (IV's, catheters, etc.) and superior skills at dealing with difficult patients early on in clinical education.