Here are some states where there have been recent high-profile challenges to the lethal-injection death penalty method:

California: A federal judge has suspended executions until prison officials fix the deficiencies he identified in the lethal-injection process.

Maryland: Executions were halted in June as new execution protocols submitted by Gov. Martin O'Malley are examined by a legislative panel. O'Malley, a death penalty opponent, waited to submit the new rules in a failed attempt to give the Legislature time to repeal the death penalty.

Missouri: The execution process resumed this year for the first time in nearly four years but was stalled in June when the state's chief justice said the court was unlikely to schedule any future executions until legal challenges were resolved over the training and competence of the state's execution team.

Arizona: Executions have been on hold since 2007 as the U.S. Supreme Court reviewed Kentucky's lethal-injection method. Kentucky's plan was approved, but the high court didn't rule on methods in other states. Federal public defenders in Phoenix then questioned Arizona's methods in state and federal court.

Tennessee: A federal appeals court delivered a victory for the state's lethal-injection method in July after executions had been held up for years by an inmate's lawsuit contending it inflicted unnecessary pain.