The negotiations, which began early this year, were led by Messrs. Booker and Scott and Rep. Karen Bass (D., Calif.). A previous effort to pass policing rules had ended in partisan acrimony before the 2020 election, but the trio, comprising three of the most prominent Black lawmakers in Congress, had been optimistic they could come to a compromise this year by focusing on areas of agreement between the two parties.

As talks progressed, however, the lawmakers were unable to resolve differences over how police officers should be prosecuted and held liable, including whether to change or eliminate a legal doctrine known as qualified immunity that shields officers from lawsuits. Democrats favored more sweeping changes, while Republicans sought more incremental moves. Even the areas they broadly agreed on—such as limiting the transfer of military equipment to local departments and the use of no-knock warrants—ran into opposition when language was drafted, according to people familiar with the matter.

“The goal from the very beginning was to get meaningful reforms that would end the policing problem we’ve had in this nation for generations,” Mr. Booker said in an interview with The Wall Street Journal Wednesday. “But in the end we couldn’t do it, if you just take some of those issues of transparency, professional standards and accountability, we couldn’t get there.”