Because that word is used to describe some terrorist action does not mean that its legitimate usage should be dropped. If anyone would have checked they would have seen that the media has been using that word to describe Obama's campaign for some time now and the following are only a few instances:
http://www.rockymountainnews.com/news/2008/feb/05/hope-for-obama-reaches-the-coasts/ "As the clock ticked down toward today's coast-to-coast contests, Obama's insurgent campaign has been buoyed by new poll results showing the national contest tightening."
http://www.westmonster.com/2008/02/obama_what_its_gonna_take.html "So, there you have it. Obama's insurgent campaign has, from the very beginning, been a long shot. And it yet could work out for him, but he has to deliver on the expectations, not screw up, and surprise everyone in either Ohio or Texas. That's a perfect storm, and it will not be easy for him."
http://www.guardian.co.uk/world/2008/jan/09/hillaryclinton.usa1 "That participation, and the demonstration of sympathy for Clinton, succeeded in halting Obama's insurgent campaign in its tracks."
http://firstread.msnbc.msn.com/archive/2007/07/25/289133.aspx "The Politico writes that Obama’s camp is planning a classic insurgent campaign “to wrest the Democratic nomination from Hillary Rodham Clinton"
http://www.sptimes.com/2007/05/13/Opinion/The_easy_case_for_Pre.shtml "Clinton remains the favorite for the nomination, but her aura of inevitability collapsed last month when finance reports showed Obama's insurgent campaign had actually outraised the New York senator, nearly $25-million to $19-million."
http://www.arkansasnews.com/archive/2008/01/30/DavidJSanders/345080.html "Nearly five years before Bill Clinton would be fighting off Barack Obama's insurgent candidacy on behalf of his wife's presidential candidacy (and his own legacy)"
"Smart! And into all those exotic mystiques -- The Kama Sutra and Chinese techniques. I hear she knows more than seventy-five. Call me tomorrow if you're still alive!"