Hillary Clinton speaks about national security issues at the Council on Foreign Relations. (Justin Lane/European Pressphoto Agency)

IT’S NO surprise that President Obama’s Republican critics have been accusing him of an inadequate response to the Islamic State. Their comments have run the gamut, from the repugnant (e.g., Donald Trump’s refusal, which he disavowed under fire, to rule out a “database” to track all U.S. Muslims) to the more substantial (Jeb Bush’s call for an “increase [in] our presence on the ground” in the conflict area).

What is a bit more surprising, perhaps, or at least counterintuitive, is that the likely 2016 Democratic presidential nominee has put distance between herself and Mr. Obama. Not only is Hillary Clinton a member of Mr. Obama’s party, but she is also his former secretary of state, closely linked to his foreign policy record. Yet in a speech Thursday to the Council on Foreign Relations, Ms. Clinton described the Islamic State as “demonstrating new . . . reach and capabilities,” and the appropriate U.S. policy goal as “not to deter or contain” the group but to “defeat and destroy” it. The contrast between Ms. Clinton’s remarks and Mr. Obama’s more limited objectives and more upbeat progress report was implicit but clear.

And it was appropriate. Ms. Clinton has a strong claim to express her differences with Mr. Obama, since it’s well-known that she argued them privately during her time in the administration, especially about how to handle Syria. (She favored more substantial U.S. support to dictator Bashar al-Assad’s opposition early in the popular uprising that has since devolved into civil war.) Not only that, but it’s clear from events in Paris that any progress Mr. Obama’s approach has achieved so far — and there has been some — is insufficient to stop the Islamic State from sowing terror far beyond the Middle East. Finally, the measures Ms. Clinton endorsed, such as safe zones, directly arming Kurdish and Sunni tribal forces if the Iraqi government won’t, and a more aggressive use of airstrikes and Special Operations forces, enjoy the backing of many military experts.

To be sure, some of Ms. Clinton’s disagreements with current policy are differences of tone and emphasis. For that reason, too, they are laudable. Though consistent with her known record, her more aggressive approach is not necessarily consistent with her short-term political interest in a Democratic primary contest that she leads by a wide margin but still hasn’t won — and which dovish voters dominate.

She is right not to pander and to push back against the wishful view that the Islamic State can be dealt with at little or no cost to the United States. That was epitomized in the remarks of Sen. Bernie Sanders (I-Vt.) the same day as Ms. Clinton’s, in which he called for “destroying” the Islamic State but suggested that it “must be done primarily by Muslim nations.” If those countries were either willing or able to do the job, it would have been done by now. Ms. Clinton, by contrast, announced that the United States “must lead the world to meet this threat.” In the weeks ahead, serious candidates of both parties will debate how, not whether, to do so.