San Francisco Mayor Gavin Newsom (D) announced Tuesday he's running for governor of California, and took to Twitter to ask supporters to spread the word.

Newsom tweeted via text message:
It's official- running for Gov of CA. Wanted you to be the first to know. Need your help. Check out video: and ReTweet

By asking followers to "retweet" the message, Newsom has gotten to one of the core uses of Twitter for politicians. The San Francisco Mayor's almost 275,000 Twitter followers can help make Newsom's announcement go viral in a matter of moments.

For a politician, that's a powerful tool.