@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 per cent of American adults have joined the site — it's become an essential tool for campaigns to test-drive themes and make news with a group of politically wired "influencers" who process and share those messages with the broader world.

Put simply: When a voter is exposed to any information related to the presidential contest, chances are it's been through the Twitter filter first.

'Teach your parents how to tweet!'—Barack Obama

"The subset of people on Twitter may be relatively small, but it's a politically engaged audience whose influence extends both online and off," said Heather LaMarre, a University of Minnesota communications professor who studies social media. "It's not the direct message that has the biggest influence on people — it's the indirect message."

No one believes the campaign will be won or lost on Twitter — it's just one slice of an enormous communication effort the presidential campaigns are waging in cyberspace. But with a well-timed 140-character blast, candidates influence coverage, respond to charges or reinforce talking points.

This, of course, is not the first time technology has changed the way campaigns are conducted. Radio, TV and the internet all prompted campaigns to adapt, giving both more avenues to reach voters and more control of their message. But radio and television are top-down mediums at heart — from the broadcaster to the public. Never before has a grassroots technology like Twitter given both voice and power to millions — and given candidates a real-time way to monitor the effects of their messages and recalibrate on the fly.

And that means an ever-changing campaign narrative for 2012.

Twitter relatively insignificant in 2008

Four years ago, Twitter was still in relative infancy and just 1.8 million tweets were sent on Election Day 2008. Now, Twitter gets that many approximately every eight minutes.

Obama's 2012 State of the Union address drew 800,000 tweets, Twitter said. And tweets mentioning Rick Santorum jumped from 10-20 per minute to over 2,500 tweets per minute when news broke that he was suspending his bid for the Republican presidential nomination.

Both the Obama and Romney campaigns have actively embraced Twitter, using it to communicate directly with supporters and, more importantly, drive the political conversation in a way that reaches far beyond the site. They're also mindful of the hazards of Twitter, designating war room staffers to monitor the site for problems to address or gaffes from their rivals to exploit.

"Our team understands that the most important issues in this campaign are jobs and the economy, not the Twitter controversy of the day," Romney spokesman Ryan Williams said. "But we need to be on top of everything and monitor every aspect of this race. Twitter helps us keep our finger on the pulse of the fast moving pace of new media.

Obama campaign showcases hypothetical woman #Julia

Twitter's impact was on vivid display last week.

Obama, warning a college audience that interest rates on their federal student loans could double if Congress doesn't act soon, urged students to make their voices heard on Twitter.

"Tweet them! Teach your parents how to tweet!" Obama said, asking them to add the hashtag #dontdoublemyrate.

The Obama campaign's introduction of a campaign tool named Julia also showcased what both parties will do to get the last word on Twitter.

The Obama team unveiled an interactive slideshow on its website showing a hypothetical woman named Julia whom the campaign says would benefit from the president's policies throughout her life.

"Follow Julia from age 3 to 67," the Obama campaign tweeted with a link to the tool — all but guaranteeing a level of buzz among Twitter users that then spilled into other social media and into reporters' stories.

Republicans, for their part, moved quickly on Twitter to respond — tying Julia to the persistent weak economy.

"Did u tell #Julia how much debt you left her?" Republican National Committee spokesman Sean Spicer tweeted.

"Based on today's bad unemployment report, it appears that Julia has given up looking for work," former George W. Bush spokesman Ari Fleischer tweeted after Friday's unemployment figures showed tepid job growth.