Robby Mook, Jeanne Shaheen's new campaign manager, sent out an "urgent video message" yesterday to her supporters, asking for an extra half-million dollars to respond to attacks by "outside right-wing groups."  

During the two-minute video, Mook notes that U.S. Sen. John Sununu leads Shaheen in cash on hand by more than $3 million. Sununu currently sits on roughly $5 million, according to second-quarter Federal Election Commission reports. We all know Senate races are expensive, but how important is this $3 million gap? Is a $5 million war chest overkill?

To start to answer that question, let's keep in mind how expensive it is to advertise on television in New Hampshire.  Campaigns advertise locally, of course, on WMUR. But to reach all the eyeballs in southern New Hampshire, Boston television is also a must. And to be thorough, throw in ad buys at stations in Portland, Maine, and Plattsburgh, N.Y.

In the weeks prior to the New Hampshire primary, for example, top-flight campaigns such as those of John McCain, Mitt Romney, Barack Obama and Hillary Clinton regularly spent at least $250,000 a week on advertising in Boston and on WMUR. Those numbers skyrocketed in the last days before the primary.

Based on those numbers, let's guesstimate that Shaheen and Sununu will spend at roughly this rate during the fall -- $300,000 a week on average, to be conservative. There are nine weeks between Labor Day and Election Day (if they wait until after the state primary, eliminate one week of spending). That works out to a bill of $2.7 million for each candidate before one spends a dollar on direct mail. Or radio. Or cable television. Or staff. 

Ad-buy arithmetic explains the urgency of Mook's appeal.  Given the burn rate of the Shaheen campaign so far,     compared to that of Sununu's, every dollar counts. 

Dante Scala teaches American politics at the University of New Hampshire and blogs at Graniteprof.