"Legal experts with varying perspectives on the rule agree that the DOL likely does not have authority to apply fiduciary duties under Title I of [ERISA] to individual retirement accounts [IRAs].... Kendra Isaacson ... former Senate pension policy director for Senator Patty Murray ... says, 'the IRA is a creature of the [Internal Revenue] Code,' and under the authority of the Treasury Department. She adds, 'If DOL wanted to cover these rollovers, it should have been a joint rulemaking.' "