s.replace string method, looping through a string

I am attempting to write a method that replaces every occurrence of a letter after the first as a "*" instead of the letter. Examples: "babble" yields "ba**le" "that" yields "tha*"

My code seems to be having an issue with the replace function while looping and I can't quite figure out why.

def fix_start(s):
    if len(s) < 2:
        s = "" 
    else:
        for i in s:
            if i == s[0]:
                if s[0]:
                    continue
                s.replace(s[i], "*")
                i += i
    print(s)