The project had a budget of just $100,000, in a race that cost approximately $51 million, including the primaries, according to Federal Election Commission records.

But however modest, the influence effort in Alabama may be a sign of things to come. Campaign veterans in both parties fear the Russian example may set off a race to the bottom, in which candidates choose social media manipulation because they fear their opponents will.

“Some will do whatever it takes to win,” said Dan Bayens, a Kentucky-based Republican consultant. “You’ve got Russia, which showed folks how to do it, you’ve got consultants willing to engage in this type of behavior and political leaders who apparently find it futile to stop it.”

There is no evidence that Mr. Jones sanctioned or was even aware of the social media project. Joe Trippi, a seasoned Democratic operative who served as a top adviser to the Jones campaign, said he had noticed the Russian bot swarm suddenly following Mr. Moore on Twitter. But he said it was impossible that a $100,000 operation had an impact on the race.

Mr. Trippi said he was nonetheless disturbed by the stealth operation. “I think the big danger is somebody in this cycle uses the dark arts of bots and social networks and it works,” he said. “Then we’re in real trouble.”

Despite its small size, the Alabama project brought together some prominent names in the world of political technology. The funding came from Reid Hoffman, the billionaire co-founder of LinkedIn, who has sought to help Democrats catch up with Republicans in their use of online technology.