Final answer:
Nixon dealt harshly with antiwar protesters by authorizing secret bombing campaigns and with civil rights activists through legislative and legal opposition to racial desegregation and voting rights.
Step-by-step explanation:
The groups that President Richard Nixon dealt harshly with included antiwar protesters, and those involved in the civil rights movement.
Nixon's politics often coalesced law and order rhetoric with action as his administration sought to undermine dissent against the Vietnam War and to stifle the progress of civil rights.
Key examples of Nixon's harsh policies include the secret bombing campaigns in Cambodia and Laos, attempts to block extensions of the Voting Rights Act of 1965, and opposing measures like school busing designed to achieve racial desegregation.