Twitter plays outsize role in 2012 campaign

NEW YORK — @BarackObama is on Twitter. So is @MittRomney. And so are all the voters following the 2012 presidential contest, whether they know it or not.

Candidates, strategists, journalists and political junkies have all flocked to Twitter, the social networking hub where information from the mundane to the momentous is shared through 140-character microbursts known as tweets.

While relatively few voters are on Twitter — a study by the Pew Research Center found that about 13 percent of American adults have joined the site — it's become an essential tool for campaigns to test-drive themes and...