Just like Pelosi, Reid, and millions of other millionaire and billionaires. The US tax rate is too high to compete with other countries. So wealthy people leave money overseas if we plan to reinvest it. We only bring it home if we need it to invest in the US. That is rarely the case since we can usually find money that is already in the US (borrow for a lower rate than the tax), or just reinvest outside the US if it doesn't matter where our new company is located. That's why my tax plan is to lower rates and close loopholes. We can get the tax rate competitive so that it makes more sense to bring money home than leave it overseas. Once the money is home, it is more likely to be invested at home, which creates jobs. And by closing loopholes we will not decrease the share of the budget that is paid for by the wealthy.

It brings Romney's tax plan into the discussion, but probably not in the best way for Obama.
I don't buy Romney's numbers, but I think it is in the US interest to lower tax rates some amount and decrease loopholes to lower the financial incentive to keep money overseas. Pointing out Romney's foreign accounts is an acknowledgment of this need to lower taxes to be competitive but is counter to what Democrats usually argue, so probably better to not bring it up.