Airlines grounded flights. Operators of 911 lines could not respond to emergencies. Hospitals canceled surgeries. Retailers closed for the day. And the actions all traced back to a batch of bad computer code.

LAS VEGAS — The phalanx of Black and Hispanic Democrats that has closed ranks around President Joe Biden as much of the rest of their party seeks to push him out of the presidential race has another goal: ensuring that if he does go, Kamala Harris will take his place at the top of the ticket.

Donald Trump has long been a man undone by himself.

BUTLER, Pa. — Before Saturday, when Butler, Pennsylvania, became the latest stunned backdrop for the nation’s political fury, Mayor Bob Dandoy thought of his town as a place that had learned to work around party lines. A Democrat in a Republican stronghold, he had campaigned on consensus.

Nearly two-thirds of Democrats said President Joe Biden should step aside and allow the party to select a different nominee, according to a new poll from the AP-NORC Center for Public Affairs Research.

As president, Donald Trump’s sweeping attempts to roll back federal environmental regulations were often stymied — by the courts, by a lack of experience, even by internal resistance from government employees.

WASHINGTON — President Joe Biden said in a prime-time Oval Office address Sunday that the nation needed to “lower the temperature in our politics,” saying that he deplored the attempted assassination of former President Donald Trump and feared for the direction of the country’s politics.