Is permission needed to retweet hot news?

When an aggregator like Google News publishes newspaper headlines, is the company treading on thin ice? What about aggregators that publish headlines and a one-line excerpt? What about those that simply rewrite the facts contained in the story and publish a new account in their own words?

Newspapers have long objected to these practices, arguing that they dilute the value of their own work. The argument here is about copyright law, since the sites in questions are reproducing verbatim headlines and leads. The key defense would be "fair use," though it's not clear exactly where it's limits would be. But think about our third question above, the one involving rewrites. These don't implicate copyright law, since nothing is being copied excepts the facts from the original article -- and copyright law famously does not extend to facts and ideas. Yet it's easy to see what might happen. One company might sit back, read AP stories, and simply rewrite them and market the new stories as its own, all without doing the work of actual reporting. This famously happened during World War I, and it lead to the Supreme Court's finding of a "hot news" right for journalists. In essence, the right does protect facts and ideas for a limited time in order to prevent rampant freeloading in breaking news stories.