Initially nothing. The following steps are followed before Obama does anything:
1. Democratic operatives and the BLM folks begin to agitate riots in major cities.
2. These riots spread to more and more cities on the east and west coasts, along with key cities in the interior of the country (Detroit, chicago, Dallas, Oklahoma City, etc.)
3. Hilary et al will be screaming about voter fraud, pointing to the riots as "voters' frustration."
4. THEN Obama will declare martial law and send the National Guard into the cities to enforce order.
5.Under martial law, Obama will cancel the inaugural "until the concerns about the election are resolved."
You left out assassination of Trump, I don’t believe the forces against him will go peacefully. Pray for protection,