Haley Stevens (D-Mich.) was up early Thursday morning, after working late Wednesday night. This was no ordinary day, in no ordinary time, for the co-president of the biggest class of freshman House Democrats in more than four decades — and the most diverse class ever.

Her morning had begun as it often does, with a look at the news and a run. But this run took her to her office in the Cannon Building on Capitol Hill to pick up something she had forgotten the day before. When she got there, she paused a few minutes at her new desk, to think about past and future. “I was reflective this morning,” she said. “I gave myself time to reflect.”

After Stevens won her election in a suburban Detroit district previously represented by a Republican, her stepfather gave her a present: copies of the Constitution and the Bill of Rights. They were on her desk on Thursday morning, and she opened them to take a look. She went to her computer, to recall what had happened 100 years ago this year. Among the milestones of 1919 was congressional passage of the 19th Amendment, which gave women the right to vote.

Newly elected House Speaker Nancy Pelosi (D-Calif.), speaking to the full House on Thursday, described the freshman class as “transformative.” The Class of 1974, the Watergate babies, arrived in bigger numbers in the election after Richard M. Nixon resigned the presidency, but this class has distinctions that the earlier class did not. “The Class of ’74 were the reformers,” said Stevens, 35. “We are the doers. We’re the defenders of democracy. We’re here to make it work.”

Those are bold words, which reflect the ambition and the confidence of the newly elected House Democrats whose elections were powered by thousands and thousands of newly activated citizens, an overwhelming number of them women. They reflect, too, the determination to make a difference. Whether the Class of 2018 lives up to the expectations they and others have set will be one of the significant stories of the coming few years.

The new class of Democrats represents a new generation, younger as a group than other classes and more reflective of a changing society. Many will be representing constituencies that long elected Republicans to Congress in suburban districts across the country.

Their ranks include a former secretary of health and human services (Rep. Donna Shalala of Florida), and a woman in her 20s and one who just turned 30 (Reps. Alexandria Ocasio-Cortez of New York and Abby Finkenauer of Iowa). There are the first Native American women and Muslim women elected to Congress. The group includes a pediatrician, a former professional football player (Colin Allred of Texas, who, with Stevens, is co-president of the class) and many with national security experience, including many women.

Two hours before the House was to convene, Stevens was in her office, the keys to which she had received only on Wednesday. Outside her office door, the second-floor corridor of the Cannon Building was jammed with people. Stevens’s neighbor across the hall is newly elected Rep. Andy Levin of Michigan. He will be succeeding his father, former congressman Sander M. Levin, and is the nephew of Carl Levin, the former senator from Michigan. Both older Levins were on hand for the family celebration, posing for pictures with well-wishers and with the new congressman.

The office down the hall houses Ocasio-Cortez, whose upset victory over Rep. Joseph Crowley in the Democratic primary last summer turned her into a national star, and the crush of people and cameras and reporters that spilled out of her front office into the hallway underscored how quickly she has become a point person for the progressive movement in the country.

“I think this new class is very unique,” Ocasio-Cortez told reporters in a brief scrum. “Around 70 percent of us haven’t held political office before, so I think what we’re going to see is a lot of new styles and a lot of new ways of approaching this body, and I’m really excited to see that play out all across the political spectrum.”

Stevens’s politics are not the same as those of Ocasio-Cortez. Her Michigan district is more moderate than Ocasio-Cortez’s district, and she brings to the House experience in government that many of her colleagues do not have. In 2007 and 2008, she worked for Hillary Clinton’s presidential campaign, preparing the briefing books for a politician famous for devouring reading material. In the general election, she worked for the campaign of Barack Obama and later joined the Obama administration.

She and her colleagues arrive in office with the government in a partial shutdown resulting from a stalemate between President Trump and Democratic congressional leaders. They arrive at a time of governmental dysfunction, political polarization and a special prosecutor investigating the president. Beyond that, Stevens was caught up in an international incident, the detention by Russia of Paul Whelan, who happens to be one of her constituents.

Stevens said she knows of chaotic transitions and openings. Ten years ago this month, she was working at the Treasury Department in the opening days of a new administration. “We were in the middle of an economic crisis,” she said. “GM and Chrysler were staring bankruptcy in the face. I was working on transition, entered into the halls of the Treasury Department, working off of a hodgepodge of equipment and recognizing that, if we didn’t make a decision about how to fund these companies, that they were going to liquidate.”

Democrats owe their new majority in part to a backlash against the president. But Stevens said the election was about more than that. Taxpayers are tired, she said, of paying for dysfunctional government. “The American people do not want dysfunction,” she said. “They want the government to work for them, and they expect that of our House of Representatives.”

There are different views of how to accomplish that among the new freshmen Democrats. Some will challenge the institution from the outside. Others will burrow into their jobs and pursue their goals in more traditional ways. But, collectively, the new class is steeped in the ways of a new generation, comfortable with social media and more informal ways of communicating. They are likely to bring change to the institution.

Stevens, like many of her colleagues, made an explicit generational appeal in her campaign and called for a new generation of leadership. When House Democrats met to elect their leaders in December, she did not vote for Pelosi to become speaker. But she made clear at the time that she would vote with her party when the full House took a vote on a new speaker, and at 1:38 p.m., standing up with a young cousin, she cast that vote for Pelosi.

Stevens said her interactions with Pelosi have been positive. “I said I’m going to go otherwise in the caucus but I’m not going to abandon you on the floor,” she said. Meanwhile, every other woman up for a leadership post in the caucus got her vote.

Stevens recalled a moment during her last day in Michigan before flying to Washington. She was on her normal morning run. “I thought about what I’m about to go do — I’m going to get on the airplane, get out to D.C.,” she said. “In two days, I’m going to be sworn in with this amazing group of people. . . . And I lost my breath. I started to choke up, thinking about the significance of this class — the never-evers, people who have never served in office, history makers, people who are pushing towards progress.”

Shortly before 3 p.m., Stevens and all her colleagues took the oath of office on the House floor. Now the real work begins. There is a government to reopen, a president who will continue to present challenges, investigations to come, a special prosecutor’s report in the offing, constituents to serve. “You asked me about my day and how I’m feeling,” Stevens said as she prepared to greet friends and relatives. “My head’s down. I’m here to do the work. I’m ready to do the work.”