A friend made an argument that I thought was fairly strong but had fairly easy lines of attack available against it. (Whether or not these lines of attack are strong/valid is unknown.) Is there a good word or phrase that would describe this proposition of his? The best phrases I can think of are "potentially assailable proposition" or "an argument that may have holes in it" or "an argument potentially vulnerable to attack".
Assuming Bob is my friend who just made the argument described above, an example usage would be in response to him:
Bob, I think that is a ____.
Edit: After thinking about this more, a key point in this question is that the argument is only potentially weak but not certainly weak.