Editor's Note: (Julian Zelizer is a professor of history and public affairs at Princeton University and author, with Kevin Kruse, of the new book "Fault Lines: A History of the United States Since 1974." Follow him on Twitter at @julianzelizer. The opinions expressed in this commentary are his own. View more opinion at CNN.)

(CNN) It looks like Mayor Pete Buttigieg -- a married, gay millennial whom few voters had heard of until a few months ago -- now has a real shot at the Democratic nomination. Who would have thought that the mayor of South Bend, the fourth largest city in Indiana, could compete in one of the most crowded primary fields ever? Buttigieg, who is expected to formally launch his campaign Sunday, has emerged as a formidable candidate.

Julian Zelizer

In retrospect, his unexpected viability makes a lot of sense.

Democrats will select their candidate at a very special moment in American history. The outrage over President Donald Trump -- what he stands for and what he is doing with the office -- is immense. Fury over the way he has used his political power and the support he has maintained from a large swath of the American constituency has energized and mobilized Democrats unlike anything in recent history. Democratic Party voters are desperate to believe in the promise of American politics once again. Many live with the sense of disenchantment in the political system as a result of Trump's election. He is the antithesis of the feeling they had on election night 2008, when it appeared that the nation was moving in the right direction on certain basic questions about the character of the country.

Buttigieg is appealing to many Democrats because he represents a shift back toward this pre-Trump American character. The mayor is intelligent and thoughtful in contrast to the bombast and bluster coming out of the White House. He seems to believe in rational problem-solving and deliberation, not ongoing Twitter rants and attacks. He comes from a new generation and the very fact that his candidacy is real represents huge steps forward that the nation has taken on basic social issues. He also remains something of a mystery, which allows different parts of the Democratic electorate to see things in him that they like. Then there's his Episcopalian faith, which leans to the left rather than being a cynical conservative tool for achieving power.

While many of the Democratic candidates have qualities that appeal to Democrats, moderates, even some Republicans, Buttigieg seems to have the well-rounded appeal and the right persona to garner the support that has taken others much longer to build. He has the potential to appeal to moderates even as he has taken some specific leftward positions on issues, like eliminating the Electoral College, expanding the size of the Supreme Court, and moving toward a single-payer health care system.

Former President Barack Obama's adviser David Axelrod likes to say that voters are often looking for someone who is the opposite of the incumbent. In trying to make sense of the 2016 election, Axelrod wrote in The New York Times that Trump fulfilled the theory of politics he believed in back in 2008: "Open-seat presidential elections are shaped by perceptions of the style and personality of the outgoing incumbent. Voters rarely seek the replica of what they have. They almost always seek the remedy, the candidate who has the personal qualities the public finds lacking the departing executive." Although this is not an open-seat election, Buttigieg (among other Democrats) does fulfill this model.

The mayor's supporters can look to the fact that there have been a number of instances in recent history in which the candidate with the least name recognition and experience has won the nomination -- and the presidency. Certainly, Democrats can think back to Jimmy Carter in 1976, a nationally unknown governor from Georgia who competed against a field of Democrats with immense experience. "Jimmy Who Is Running for What!?" read the headline of the Atlanta Constitution during Carter's candidacy.

Understanding better than anyone why voters yearned for a candidate whom they could trust and someone who did not seem deeply enmeshed in Washington politics, he won the nomination and he won the presidency. In fact, he titled one of his campaign films "Jimmy Who?" just to prove a point. Carter also had a keen feel for the dynamics of the post-1960s news media and nomination process, which helped him figured out how to catapult victories in small contests like Iowa into broad support.

Obama had a similar experience in 2008. The senator, without a lengthy record in elected office, took on a political giant, Hillary Clinton. Added to this was the open question of whether the country would vote for an African-American president, which was not clear given our country's long history with racism. In the end, voters gravitated toward Obama, eager for a figure who they could believe in -- one who promised to move the nation beyond the broken, polarized, divisive and dysfunctional world they read about in the news every day. The clarity he showed in his opposition to the Iraq War in 2002 offered a stark contrast to Clinton's middle-of-the-road stand.

With the bleak atmosphere created by the ongoing war in Iraq, as well as total collapse of the financial system in the fall of 2008, Obama was a refreshing political figure. And so he won the presidency.

Some would say Trump's nomination and victory also reflects how unpredictable our presidential elections have become and how a candidate who resonates with certain portions of the party can win the nomination despite conventional wisdom. Though there are debates about the sources of the sentiment behind his success, there is agreement that a particular brew of economic and identity anxiety led Republican voters to flock toward him over much more established candidates, like Jeb Bush, providing enough support for Trump to win the Electoral College.

We are far from a place where we have a clear picture of what Buttigieg's future holds. This could be a rise-and-fall candidacy that fizzles by the time we are into the summer. We have seen many of those in recent years as well. And Buttigieg still has many questions to answer about the substance of his ideas, his capacity to handle this job given his minimal experience, and whether he has the tenacity to withstand the blistering attacks that will soon be coming his way. He will also face some very strong candidates who are smart, savvy.

But it would be a mistake to quickly discount the possibility that his campaign can be a formidable one. Not only have we seen similar stories, but we are living in one of those unique moments in which many Americans feel a sense of disillusionment, crisis and fear, like 1976 and 2008. They are desperate to believe things can be different and desperate to believe in the character of politicians.

Yes, they want a tough partisan fighter who won't blow the campaign, but they also want that fighter to be someone who inspires them and makes sure that people come out to vote. That feeling is what gives the mayor from South Bend his opening to at least make a serious play for the nomination.