The World Cup has historically been a boon for Twitter, bringing in record traffic and an influx of advertising dollars.But this time, when the global soccer tournament started on Nov. 20, Twitter’s U.S. ad revenue was running at 80 percent below internal expectations for that week, three people with knowledge of the figures said.In tandem, Twitter was rapidly cutting its revenue projections. The company previously forecast that it would generate $1.4 billion in the last three months of the year, down from $1.6 billion a year ago because of the global economic downturn. But as Twitter kept missing its weekly advertising targets, that number slid to $1.3 billion, then to $1.1 billion, two people said.Elon Musk, Twitter’s new owner, has warned repeatedly that his social media company faces …
