The main thing is that he should remember that given where the polls stand, a tie tonight is a big win for his campaign, and even a narrow loss won’t hurt. If you debate a sitting president on foreign policy and he doesn’t blow you out of the water or make you look silly, you’ve won. You’ve passed another threshold test and demonstrated that you have what it takes to perform at a presidential level on foreign affairs. The essential nature of this race hasn’t changed; there are enough voters out there who aren’t thrilled with the Obama presidency to deny him a second term—if the alternative looks credible.
To look credible you don’t have to skewer the President or make him look like a total failure, and you don’t have to show in detail how he’s done wrong. If you hold your own and land a few punches, you’ve done what you needed to do.
To accomplish that, Romney’s best strategy is to surprise the conventional wisdom and to campaign as a man of peace. John McCain made a lot of mistakes in his 2008 campaign; one of the largest was letting the Obama campaign own the peace issue. Voters in 2008 didn’t want to hear how tough and unrelenting the next president would be; they wanted to hear how the next president would work to create peace without sacrificing their security.