As the budget deficit increases, the demand for loanable funds increases causing the interst rate to rise. The rise in the interest rate attracts foreign investment, rasing the capital account. Since the capital account and the current account must always be in balance, as the capital account rises, the current account falls meaning the trade deficit increases. This is the main reason for the huge explosion in US trade deficit in the 1980s, foreign capital was rushing in becasue of the large government deficits leading to a need to import more goods.
This is why I'm more worried about the budget deficit. The trade deficit will work itself out through price mehcanisms fairly easily. However, the US was somewhat protected in the 1980s from facing the full cost of the budget deficit. This is for two reasons. The first is that Social Security and Medicare were running surpluses, meaning there was an automatic increase in the demand for US bonds, keeping the interest rates lower than they otherwise would have been. The second is that there was alot of foreign capital willing to move to the US in the 1980s, so interest rates did not have to move as high to bring it in. However, since the 1980s, foreign investment markets have become more liquid and there are now investment opportunities that really weren't available through out the 1980s, especially at lower levels of risk. So Social Security will actually be selling bonds in the next decade and there are many otehr opportunities for foreigners to invest in. These two combined lead to higher cost of a budget deficit then we faced previously. And so if the Fed maintains a near zero inflation rate target, we may see really high real rates over the next decade if the deficit continues to expand.