A ruling in January by Iraq’s highest court — sought by Mr. Maliki — gave him control of once-independent agencies responsible for running the country’s central bank, conducting elections and investigating corruption.

A month after that ruling, two leading human rights groups reported that forces that report directly to Mr. Maliki in violation of the country’s constitution were running secret jails where detainees had been tortured.

And in July, Iraq’s high court ruled that members of Parliament no longer had the power to propose legislation. Instead, all new laws would have to be proposed by Mr. Maliki’s cabinet or the president and then passed to the Parliament for a vote.

Political experts said they knew of no other parliamentary democracy that had such restrictions.

With influence from the United States waning as the military prepares to withdraw at the end of the year, Mr. Maliki’s critics say that one legacy of the eight-year American occupation is a democratically elected leader from the country’s Shiite majority who has far more power than its Constitution intended.