Elected on the heels of global protests over police brutality, President Joseph R. Biden Jr. promised broad reform to American policing.

He pledged to step up the use of the strongest tool for overhauling problem-plagued police departments, beginning sweeping civil rights investigations into a dozen police forces, including in Minneapolis, Trenton, N.J., and Louisville, Ky.

So far, those investigations have produced 551 pages of findings full of shocking examples of brutality, racial profiling, illegal arrests and impunity for officers who had committed misconduct.

But the Justice Department is running out of time to convert those reports into binding plans of action.

The Biden administration has produced only one final oversight agreement, in Louisville. President-elect Donald J. Trump is unlikely to pursue more.

During Mr. Trump’s first term, the Justice Department turned away from seeking new oversight agreements and pulled back from enforcing those already in place. On the 2024 presidential campaign trail, Mr. Trump repeatedly said that he wanted to give officers “immunity from prosecution, so they’re not prosecuted for doing their job.”