Whenever taxes rates are cut on the very wealthy, federal revenues fall, and if spending cuts do not sufficiently compensate for those cuts, then there's a deficit, which means federal debt increases.
If Romney becomes Pres (which thankfully, will no longer happen), then he will cut taxes on the very wealthy (as every GOP Pres has done since 1980) and make no changes in overall spending (i. e. cut spending in some areas to make room for more wasteful military spending, as every GOP Pres has done since 1980). Therefore, under Romney, the debt will increase more than it would under Obama, who will not cut taxes on the very wealthy.
There's nothing mysterious about it: it's basic math. Conservatives just don't get it because they do not understand basic math. They're education doesn't come from a real school, but from the Limbaugh Institute, where math is not taught.
Case closed.