I infer his defenses (technically) were:
1. He did not take a substantial step toward kidnapping Speaker Pelosi.
2. He did not assault her husband as retaliation for her performing her official duties.
The jury disagreed (as would [most of] the inhabitants Earth 1).
DePape still faces the state charges, for which then-Speaker Pelosi will be irrelevant. And, yes, the state prosecutor can introduce evidence of DePape's admission in federal court that he did the attack. But it'll just be stacking excessive years on at this point; DePape will die in prison (NADT).