Question: Who was the president at the time when the opponent of Benjamin Spock held office?
SPARQL query: SELECT DISTINCT ?uri WHERE { ?x <http://dbpedia.org/ontology/opponent> <http://dbpedia.org/resource/Benjamin_Spock> . ?x <http://dbpedia.org/property/incumbent> ?uri  . }
Answer: The incumbent president of the people whose opponent is Benjamin Spock is [Richard Nixon].