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Carlos Osorio, File, Associated Press
FILE - In this Oct. 21, 2011 file photo, Republican presidential candidate, Herman Cain waits to speak in Detroit. Twitter is abuzz with presidential candidates this year, though not all in the Twittersphere are equal.

NEW YORK — Twitter is abuzz with presidential candidates this year. But on the campaign trail winding through the Twittersphere, some hopefuls are more proficient than others.

Rick Santorum tweets a lot more than Rick Perry, Herman Cain is the most likely to be retweeted, and they're dwarfed by President Barack Obama's tweet numbers.

That's according to an Associated Press analysis of the presidential candidates' use of Twitter. The AP found widely different levels of engagement, despite Twitter's emergence as key to every campaign's strategy.

The AP analyzed each candidate's Twitter stream beginning the day he or she joined the presidential contest. The data is available from Twitter's website. It highlights every message posted by candidates, as well as how many times other users on the site reposted candidates' messages.