Warner just announced he is retiring. This makes his Virginia seat the biggest race for the Senate in '08. The last one was decided by 0.00000001% (actually not quite that small) And it is presently Repub which tends to make the defending party fight even harder for it. Virginia is the race the Repubs must win to stay relevant for '08 - '10.
And then we have Larry "wide stance" Craig who is resigning in the next day or so. There will almost certainly be a Repub primary for his seat in '08 and there is a strong Dem candidate so it will be a competitive race. After Tester took Montana everyone will assume this is winnable for us Dems. So again, tons of money and effort needed there.
So who loses? Bob Schaffer who is figured the least likely Repub to win in '08. The Repubs don't have the resources or money to fight everywhere. As of today they have probably already cut him lose in their minds.
It's fun to be in the ascendancy....