WASHINGTON — Just days before Donald J. Trump raises his hand to take the oath of office, police departments in Chicago and Baltimore have agreed to federal overhauls, Cubans no longer have an easy route to residency in the United States, and new civil rights monuments in Alabama and South Carolina are on the books.

Still in the works as the seconds tick by for President Obama: a negotiated release of American hostages in Afghanistan, another lengthy list of reduced prison sentences for nonviolent drug offenders, and a raft of appointments to obscure but important federal boards and commissions.

And in the face of Mr. Trump’s repeated questioning about whether the United States was getting value for its security dollars in supporting NATO, American tanks began rolling into Poland on Thursday, making good on a promise by Mr. Obama to help Eastern European countries counter Russia’s president, Vladimir V. Putin.

Mr. Obama’s last moments in the White House are being filled with one announcement after another, each intended to bring long-planned efforts to a conclusion before members of his administration unplug their computers, turn off the lights and leave their offices for the last time.