Washington (CNN) Maryland's Attorney General on Tuesday filed papers asking a federal judge to replace Matthew Whitaker as acting US attorney general with Deputy Attorney General Rod Rosenstein.

Brian Frosh argues Whitaker was not properly appointed and his appointment violates the Attorney General Succession Act in addition to the Appointments Clause of the Constitution.

His court challenge seeks a preliminary injunction that would stop the Justice Department from proceeding in defending a lawsuit involving the Affordable Care Act unless Rosenstein replaces Whitaker.

Maryland, along with more than a dozen other states, are seeking rulings that the Affordable Care Act remains enforceable despite the Trump administration's efforts to dismantle it.

Since Maryland's lawsuit named former Attorney General Jeff Sessions as a defendant, the state now says the judge overseeing the lawsuit should declare that the proper defendant as attorney general is Rosenstein, not Whitaker.

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