Point being that popularity of the president and a war does not lead to his party gaining seats in midterm elections. Look at recent history, then. In '98 the party in power gained seats (unfortunately). Redistricting slightly favors the Pubbies, fundraising most assuredly does, and the polls look favorable (though we're still six months out).
The party in power gaining seats is a very rare occurance. If memory serves me right, 98 was only the 3rd or 4th time in history that it has happened.