I'm looking for a short story, probably from the mid '60s to mid '70s, in which two candidates, possibly senators running for president, undergo a public test of how well they perform as leaders by acting in the role of all-powerful deities to a population of tiny, perhaps microscopic, synthetic beings.

There is a bloody, brutal conflict going on in the synthetic world, analogous perhaps to that between the early Christians and Romans. One of the human contestant-gods refuses to directly intervene to prevent the execution of a "prophet", who believes god exists, but is having you might say a hard time convincing others.