Nujaifi’s position and Iraq’s two other vice presidencies were eliminated by Prime Minister Haider al-Abadi in purported cost-cutting measures announced this summer. But there is little change at Nujaifi’s office. His staff is still paid, he said, and he is working as normal.

Nujaifi’s defiance highlights Abadi’s weak hand as he fails to execute anything but superficial changes after pledging wide-ranging reforms in response to street protests. Smelling blood as he flounders, his political rivals have turned on him, while ­Iranian-backed militias leverage what they can from him.

His precarious position appears likely to raise concerns in Washington as it backs him in his fight against the Islamic State — a war that has taken on a new urgency for the United States and Europe as the group has rapidly expanded its operations overseas.

“His position is shaking,” said Ali Adeeb, a senior member of Abadi’s Dawa party. “Everyone is talking about who Haider al-Abadi will be replaced by. Perhaps the will of the big people that want this change will succeed.”