For instance: "To @SenatorCollins: Please pass health insurance reform this year http://bit.ly/3133JC #hc09 #ME #04101"
Since such tweets are visible when users search for a senator's Twitter account, it's more traceable and public than calls to a member's office. Formally, it's like clicking to send a pre-written op-ed to a local paper. Senators not on Twitter are immune.
This article available online at:
http://www.theatlantic.com/politics/archive/2009/07/tweet-your-senator-with-the-democratic-partys-help/22188/
