In declaring Tuesday that he would “finish the job” in Afghanistan, President Obama used a phrase clearly meant to imply that even as he deploys an additional 30,000 or so troops, he has finally figured out how to bring the eight-year-long conflict to an end.

But offering that reassuring if somewhat contradictory signal — that by adding troops he can speed the United States toward an exit — is just the first of a set of tricky messages Mr. Obama will have to deliver as he rolls out his strategy publicly.

Over the next week, he will deliver multiple messages to multiple audiences: voters at home, allies, the leaders of Afghanistan and Pakistan, and the extremists who are the enemy. And as Mr. Obama’s own aides concede, the messages directed at...