The contents of Romney's tax returns: What would be able to brush off?

[So rightwing that I broke the Political Compass!]

Theirs been a lot of speculation about what might inside them. Some people have suggested:
-that he's wealthier then he claims to be
-proof that he was working for Bain for longer then he claimed
-Evidence of offshoring and other tax evasion
-In substantial debt
-Failure to donate the expected tithe to his church
-having(legally) paid relatively little in taxes thanks to loopholes
(no doubt their are other possibilities, though none come to my mind)

 So which potential contents would you rank as:
a)easy to brush off
b)likely to make a dent in Rom's election performance
c)almost certainly fatal to Rom's election chances
?

[So rightwing that I broke the Political Compass!]

I doubt he failed to donate to his church at some point. If he had, he would have probably gotten in trouble with the church elders.

I know. The suggestion was that he'd donated a lower percentage then he should(my recollection is that Mormons are supposed to donate around 10%)