Mrs. Clinton remains the second-biggest name in Democratic politics, behind only Mr. Obama. No one else—not even Mr. Biden—is even close. And, so far at least, her work as secretary of state has only enhanced her stature. As she jets from one corner of the world to another (and makes headlines at every stop), Americans have gotten a chance to see her essentially acting like a president—a leader on the world stage, not just another senator making pointless floor speeches and casting procedural votes.

And by all accounts, her relationship with Mr. Obama, defined by mutual mistrust and scorn during and immediately after their campaign, is now cooperative and even friendly. It helps that she has done nothing as secretary of state to arouse suspicions of grand-standing and political posturing at Mr. Obama’s expense. She’s been the team player that many of Mr. Obama’s supporters doubted she’d ever be. In terms of ’16, this has earned her many new potential friends—and cost her none of those she already had.