Discussing foreign policy in the wake of the attack on Paris at a Democratic-candidate debate last night, Hillary Rodham Clinton gave the Republican Party a guide map to her defeat.

A Republican candidate who can effectively harness President Obama’s former chief diplomat to the Obama policies in the Middle East that have helped lead us to this dreadful pass is going to give Clinton a devil of a time.

Under appropriately polite but devastatingly persistent questioning by moderator John Dickerson, Clinton proved astonishingly incoherent.

We must “root out” ISIS, she said, and implicitly criticized Obama when she said it “cannot be contained, it must be defeated.” At the same time, she said, “it cannot be an American fight.” However, “American leadership is essential.” And yet, she said, “I don’t think that the United States has the bulk of the responsibility.”

Instead, and breathtakingly, she suggests the person who must take the lead is Syria’s dictator, himself responsible for the slaughter of hundreds of thousands of his own people and the progenitor of the refugee crisis that is turning Europe inside out: “I really put that on [President Bashar] Assad and on the Iraqis and on the region itself.”

This is nonsense on stilts, and it deconstructs itself.

If ISIS must be defeated, then by definition this is an “American fight” because it is a necessity for the good working order of the world and the safety of the United States. And if Clinton believes “American leadership is essential,” then again by definition American military leadership is essential.

You cannot have it both ways. ISIS is not going to be “defeated” unless the United States defeats it. It will not be “destroyed” — Bernie Sanders’ startling word at the debate — unless the United States defeats it.

Clinton basically endorsed our present course. “That is why,” she said, “we have troops in Iraq that are helping to train and build back up the Iraqi military, why we have special operators in Syria working with the Kurds and Arabs, so that we can be supportive.”

What we are doing now is not going to cut it. Obama knows it. That’s why the man who promised to destroy ISIS shifted to the worst timed talking point in history on Friday — saying ISIS has been “contained” just hours before the carnage in Paris began.

Her policy incoherence only became more pronounced when she intimated — jaw-droppingly — that Obama had only pulled out of Iraq and left a power vacuum there because of a status-of-forces agreement President George W. Bush had made before leaving office in 2009.

Her answers were terrible, but they were terrible because there are no better ones. And this is the Republican opening: She cannot move very far away from the president, because she was his diplomatic steward for four years.

If ongoing events make foreign policy a key voting issue in 2016, and the Republican candidate is as assured at questioning Clinton about it as Dickerson was last night, Hillary will reap the whirlwind — and the Republican will be the beneficiary.