You are right. In the last 2 election cycles Republicans seemed to surge in the end and it worked out. I hope that can happen a third time but it would be very uncommon for one party to do well in 3 consecutive elections. Still, if the GOP retains control, even by reduced margins, that is a victory.
Even if they keep a majority it will still be a very sad commentary on the state of our union when voters see fit to elect candidates who promise to oppose the president on every security issue while we are at war. It will send a bad signal to the bad guys. Not to mention it will be a bad blow to Republicans if they lose senate seats in such major states as PA, OH, or MO.