We’re covering new details about the unrest in Iran, the dwindling Democratic presidential field, and the arrest of suspects in a massacre last month in Mexico. | | By Chris Stanford | | The Trump administration reached an agreement with Canada and Mexico on revisions to the North American Free Trade Agreement last year, but the deal still needs the approval of Congress. | | The details: The deal is more progressive than traditional Republican views on trade and includes measures that Democrats have long sought. Those include requiring more of cars’ parts to be made in North America, rolling back a special system of arbitration for corporations and strengthening Mexican labor unions. | | A bank in Tehran that was destroyed during protests last month. Wana News Agency/via Reuters | | At least 180 people — and possibly hundreds more — have been killed in the past few weeks in some of the worst political unrest in Iran since the Islamic Revolution 40 years ago. | | Protests erupted after a steep increase in the price of gas was announced on Nov. 15. In the resulting government crackdown, Iranian security forces opened fire on the demonstrators. The scope of the violence is now becoming clear after an internet blackout was lifted. | | The authorities have not disclosed the number of casualties and arrests, and have denounced unofficial figures on the death toll as speculative. | | Many Iranians have directed their hostility at the country’s supreme leader, Ayatollah Ali Khamenei, who called the response a justified reaction to a plot by Iran’s enemies. | | Background: The gas price increase came as Iran struggles to fill a budget gap, created in large part by tight American restrictions on the country’s oil exports. | | Another angle: In Iraq, the formation of a new government will probably take weeks, if not months, after the resignation of Prime Minister Adel Abdul Mahdi over the weekend. He faced widespread anger over political corruption and Iran’s influence over Iraqi politics. | | The former vice president might lose the first Democratic contests in Iowa and New Hampshire, but if he maintains his strength with black voters, he will have a structural advantage that’s greater than his uneven polling lead suggests. | | Under party rules, more delegates are awarded in districts with high concentrations of Democrats. Because black people overwhelmingly vote Democratic, areas with many black residents tend to have higher numbers of Democratic delegates. | | A recent poll showed Mr. Biden at 44 percent among black voters in South Carolina, which has historically been a harbinger for how the South as a whole will vote. The same poll showed his closest competitor, Bernie Sanders, trailing him by more than 30 percentage points among black voters. | | Quiz time: Who was the last Democratic presidential candidate to win the nomination without winning a majority of black voters? The answer is at the end of the briefing. | | Queen Elizabeth II and Prince Charles at the state opening of Parliament in October. Pool photo by Toby Melville | | As Queen Elizabeth II welcomes world leaders to London this week to observe the 70th anniversary of NATO, the royal family is at a turning point. | | Prince Charles, the 93-year-old queen’s son and heir, has recently moved to take a greater role in royal affairs. Most notably, he pressed to strip his younger brother Prince Andrew of his public duties after Andrew gave a disastrous TV interview about his friendship with the convicted pedophile Jeffrey Epstein. | | Quotable: “The monarchy is a rock of stability that has served this country well in times of crisis,” said Penny Junor, a royal biographer. “But we’re coming to the end of a pretty troubled year, which adds to the woes of the family.” | | The Class of 2000 at Minford High School in Ohio started classes the year Purdue Pharma introduced OxyContin. By senior year, the painkillers were everywhere, in classrooms, school bathrooms and parties. | | To understand the scope and the consequences of the opioid crisis, The Times talked to dozens of members of the class, many of whose lives have been affected by addiction. Since they graduated, more than 400,000 Americans have died from opioid overdoses. | | PAID POST: A MESSAGE FROM LINCOLN FINANCIAL | The More You Talk, The Better You Plan | Talking about your retirement goals is the first step towards building a more secure financial future for you and your loved ones. Our new conversation kit can help you get the conversation started. | | Download Conversation Kit | | | Arrests in Mexico: Several suspects were detained in connection with the killings of nine members of a Mormon sect in the north of the country last month. | | Resignation in Malta: Prime Minister Joseph Muscat said that he would step down in January, after questions about whether his associates were involved in the killing of a well-known journalist in 2017. | | Jeenah Moon for The New York Times | | Snapshot: Above, a slushy Times Square in New York on Sunday, when heavy snow in the Northeast snarled post-Thanksgiving travel. The storm is expected to linger into Tuesday. | | Metropolitan Diary: In this week’s column, paying with cash, wondering what a subway rider is studying and more reader tales of New York City. | | Linda Xiao for The New York Times | | Go: An exhibition at the Louvre will celebrate the French painter Pierre Soulages’s 100th birthday. The only other artists given shows there during their lifetimes were Picasso and Chagall. | | File this under the category “Who Knew?” The queen in chess was not always as powerful as she is today. | | I’m Katharine Seelye, a longtime reporter for The Times and a chess player. I learned about the change in the queen’s power last week, while writing an obituary of Marilyn Yalom, a feminist author. Her 2004 book, “Birth of the Chess Queen: A History,” describes the queen’s evolution from weakest piece on the board to mistress of the universe. | | Ivory chess pieces with a Trojan War theme. Bryan Thomas for The New York Times | | When the game was first played in the sixth century in India and the Arab world, the chess queen did not exist. | | Ms. Yalom posits that those examples inspired game makers to reflect such power on the board. Initially, the queen could move only one square, on the diagonal. | | In time, the queen was granted superpowers and became the mightiest of all — at least in chess. | | That’s it for this briefing. | | The answer to the quiz question above: The last Democratic candidate to win the nomination without winning a majority of black voters was Michael Dukakis, then the governor of Massachusetts, in 1988. | | Thank you Mark Josephson and Eleanor Stanford provided the break from the news. You can reach the team at briefing@nytimes.com. | | Were you sent this briefing by a friend? Sign up here to get the Morning Briefing. | | |