On the Republican side it probably helps everyone but Ron Paul. Success in Iraq helps George W. If his approval numbers begin to climb into the mid- to high-forties then whoever the GOP candidate is runs with more confidence.
At the Congressional level, the Harry Reid (D-Nevada) wing of the Democratic Party looks even more spineless than it does today if the President's "surge" strategy continues to produce positive results.
If that is the case incumbents like Sen. John Sununu (R-NH) look decidedly stronger in their re-election bids, meaning massive Democratic increases in the US House and Senate are far less likely.
First, though, the White House has to help sell the story of success in Iraq. The White House alone has the capacity to move the Success in Iraq story from page A19 to page A1.