Just over half of Americans doubt that he pays his fair share in taxes. After hearing about his actual income and tax rate, these people are less likely to think he “cares about people like me”—an attribute on which Romney is disadvantaged relative to Obama and which is a perennial predictor of how people vote. Information about his wealth also leads a larger fraction of Americans to believe he cares about the wealthy, and this belief in turn also reinforces the sense that he does not care about “people like me.” The more Romney’s wealth and taxes are discussed, the more he may seem like someone who cannot relate to ordinary voters. This may explain why, during a time in which his wealth and taxes were in the news, negative views of Romney jumped 20 points among whites with incomes below $50,000.
And that's a key demographic for past GOP victories. If Obama can increase support among those voters, things look much bleaker for Romney/Gingrich/Whoever. My view is that this is less damaging and relevant than that Romney's economic proposals want to tilt the balance even further in favor of the super-wealthy. Maybe there's a way for him to neutralize this in some small way. Jed Graham points out that Greg Mankiw, one of Romney's top economic advisors, opposes the carried interest loophole that Romney has (perfectly legally) taken advantage of. Graham's suggestion:
Perhaps there is a route by which Romney can propose to end the tax break as part of a deal that lowers tax rates while broadening the tax base. That would narrow the gap between taxes on regular income and investment gains, thus making favorable treatment of carried interest less meaningful. But Romney has resisted putting forward a comprehensive tax reform plan, presumably because its details would create plenty of more targets for foes to attack.
If Romney were to roll out a serious tax reform plan, Obama would be in trouble.