Hillary Clinton gave a major foreign policy speech at the Brookings Institute this week that is being characterized as "hawkish" and as a break from Obama on foreign policy.
She does, in fact, say he should have been more aggressive with regard to Syria and ISIS and Russia, just as she emphasizes how she would be tough on the Iranians as the nuclear deal gets implemented. Obama is temperamentally inclined more to negotiation and compromise to get to the best solution that is possible at the time -- which is good, in my opinion.
But there's not much real policy difference between them. For example, she supports the Iran nuclear deal. This tough talk is campaign rhetoric, more than real difference. Hillary's standing in the primaries continues to slide. Bernie Sanders now ties and threatens her front-runner status in both Iowa and New Hampshire -- and she's being constantly attacked by the Republicans.
Hillary is primarily trying to show that she will be a tough president on foreign policy. And she will be. Obama's overall style has been constrained to avoid him looking like "the angry black man." Clinton needs to show that she's not a "weak woman."
Having said that, it's also true that she is more hawkish than Obama. She voted for the Iraq war; he voted against it. But she was also involved in the decision to go the diplomatic route with Iran. Then Obama had to oversee, along with John Kerry, the delicate negotiations with Iran. She didn't.
That's a big difference in what kind of sword-rattling rhetoric you use. It's as much to do with that as with the substance of policy.