Attorney General Jeff Sessions’s decision this week to review concessions by local police departments accused of misconduct is part of a seismic shift at the Justice Department, which has quickly changed its emphasis under the Trump administration from protecting civil rights to promoting law and order.

Mr. Sessions is poised to be one of the most powerful members of President Donald Trump’s cabinet as the president seeks to dismantle President Barack Obama’s legacy on a wide range of issues, including criminal justice.

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