How can an Incumbent put down a Primary Challenge?

Well, if you are Democrat Senator Maria Cantwell of Washington State, you just pay off your opponent with an over-paid staff job on your campaign. From the Seattle Post-Examiner:

Cantwell pays former opponent $8,000 a month
Campaign manager makes only a little more

A vocal former opponent's silence is important enough to Sen. Maria Cantwell's re-election effort to pay him $8,000 a month -- nearly as much as her campaign manager -- to join her campaign staff.

The Cantwell campaign initially refused to say last week how much it would pay Mark Wilson to drop his Democratic primary challenge to the senator and his harsh criticism of her opposition to immediate U.S. military withdrawal from Iraq.

But campaign manager Matt Butler issued a statement Thursday disclosing Wilson's salary.

It isn't much lower than Butler's salary, which, according to Cantwell's quarterly Federal Election Commission report, was $26,192 for the first three months of 2006, or $8,731 a month.

She still has one challenger, I wonder if they have more positions open on her campaign staff?