Julian Zelizer is a history and public affairs professor at Princeton University and the editor of "The Presidency of Barack Obama: A First Historical Assessment ." He's also the co-host of the "Politics & Polls" podcast. Follow him on Twitter: @julianzelizer . The opinions expressed in this commentary are his own.

(CNN) Barack Obama has been out of the White House for only a little more than a year. But it's not too soon for historians to begin to assess the impact of his momentous presidency. Soon after the election, I convened a conference at Princeton University to start the discussion, and now some of the work by scholars who attended the meeting has been published as the first historical assessment of the 44th President's two terms. In the piece that follows and with the contributions from some of the historians, we attempt to analyze what Obama did and did not accomplish.

To begin, any assessment of President Obama has to reckon with the extraordinary election that resulted in the election of Donald Trump as his successor, a President who has seemed determined to erase Obama's legacy. Obama's failure to see it coming -- in this he was not alone -- is one of the biggest question marks over his White House years.

What Obama could never accept about American politics was just how ugly it had become. In many ways, this always had been the President's greatest political weakness. His confidence in our democracy prevented him from doing more to stand firm against the destructive forces that were shaping our country during his two terms in office. Obama's election in 2008 was supposed to signify that our country was finally moving in the right direction -- a country born with slavery had elected an African-American to be president.

As President, Obama never let go of this hope. That was what made him so endearing to millions of Americans and shaped much of what he did in the Oval Office. Obama had clearly articulated his understanding of the nation when he came into the spotlight during the Democratic National Convention in 2004.

In the middle of one of the most contentious moments of the era, when Americans were deeply divided over a President who had taken the nation into a costly war in Iraq based on false claims of Weapons of Mass Destruction, then-Illinois Sen. Obama refused to give in to anger and disillusionment. "Even as we speak, there are those who are preparing to divide us, the spin masters and negative ad peddlers who embrace the politics of anything goes. ... But I've got news for them, too. We worship an awesome God in the Blue States and we don't like federal agents poking around our libraries in the Red States. We coach Little League in the Blue States and have gay friends in the Red States. There are patriots who opposed the war in Iraq and patriots who supported it. We are one people, all of us pledging allegiance to the stars and stripes, all of us defending the United States of America."

During his first year in office, as Republicans spoke about incessant obstruction and refused to join him on legislation, whether the debate centered on rescuing the plummeting economy through a stimulus package or trying to fix a broken American health care system, Obama kept reaching out to shake their hands. Every time that they bit him rather than agreeing to compromise, Obama gave bipartisan civility another shot.

Many members of his party pleaded with him to stop watering down his proposals, including lowering the amount of his stimulus request, based on the false hope he would be able to persuade his opponents -- but Obama insisted. As the political ecosystem started to drown in partisan spin and vitriolic slander, he attempted to be reasonable, appealing to the evidence-based angels in our electorate, desperately trying to ignore all the noise.

But the partisan noise was what our politics was now about. And this influenced much of his term in office. Starting with the 2010 midterm elections, Obama was Tea-Partied. He watched as the Republican Party veered far to the right. A new generation of politicians came into power whose core policy beliefs were well outside the mainstream. They were extraordinarily hardline in their stance against immigration. They had little tolerance for criminal justice reform to achieve racial justice. They hated the Affordable Care Act and financial regulations. And they were determined to cut federal spending as much as they could.

The style of the Tea Party Republicans was as notable as their agenda. They believed in a kind of ruthless form of political combat, where they went so far as threatening to send the nation into financial default over spending disputes, shocking some senior members of their own party. Senator John McCain, R-Arizona, called them " Tea Party Hobbits ," a reference to The Lord of the Rings, that was based on "crack political thinking."

And the Tea Party generation vehemently hated the entire political establishment -- Republicans and Democrats. They refused to listen to anyone other than themselves. When they no longer needed a specific person as leader, like Speaker John Boehner or Majority Leader Eric Cantor, they were prepared to pressure him out of power. The Tea Party also built a strong grassroots political operation and amassed substantial financial support, so they were a force to be reckoned with. Far-right extremist groups, who Obama's election was supposed to have been a repudiation of, continued to circulate in these conservative circles.

While Obama spoke calmly about facts and data, Tea Party Republicans operated in a conservative media universe that privileged screaming, yelling, attacking and just making things up if they fit into a specific world view. In the political media world where the Tea Party thrived, it was possible to say that the first African-American President might be illegitimate based on false accusations that he was not born in the United States.

Whereas this kind of fractious media conversation had always existed on the margins, now these kinds of stories could be seen, heard and read on powerful networks and websites. This wasn't the Yellow Press -- it was the mainstream press. The "birther" controversy, for instance, actually received coverage on mainstream networks. A politician like Obama could be civil as much as he wanted, but nobody on these airwaves would be listening. The point was to preach to the converted, to strengthen their view of the world rather than trying to challenge or to inform.

Obama understood that the worlds of reality television and national politics were becoming dangerously intertwined, but he had faith that the more serious voices among us would ultimately prevail.

Tea Party Republicans were also incredibly sophisticated at using political institutions to their advantage. They mastered the art of gerrymandering by relying on sophisticated computer technology to build solidly red districts after having scored huge gains in state and local elections in 2010. Republicans pushed draconian voting "fraud" laws in states such as Arkansas, Georgia and Wisconsin that disenfranchised Americans who tended to vote for the Democrats -- and this despite there being no evidence of any real problem in elections.

More was going wrong between 2009 and 2017 than the dangerous drift of the GOP. The campaign finance system completely broke down. The Supreme Court's Citizens United decision (2010) essentially legitimized a system in which private money dominated elections. The Koch Brothers became the most visible manifestation of this problem. Obama understood that this was a serious problem, but he didn't do much to really solve it. Government reform was never a top priority.

He saw firsthand how the overwhelming power of lobbyists in Washington could stifle progress on legislation that a majority of the nation wanted, as was the case when the National Rifle Association repeatedly killed gun control legislation each time there was a horrific shooting. The commercial forces behind the prison-industrial complex that greatly damaged African-American communities had no interest in tackling the kind of institutional racism he understood was at the heart of the police shootings of African-American men that shot the nation.

But he could not come to terms with these elements of American politics. And he found his presidency severely constrained after 2010, when the Democrats lost control of Congress.

His second term, of course, ended with Donald Trump emerging as his successor. Trump embodied a great deal of the political dysfunction in our democracy that Obama refused to acknowledge. Trump's victory, which was a product rather than the cause of our politics, represented a direct repudiation of Obama's promise in 2004.

Just like Obama has watched as his policy agenda has quickly unraveled and a style of combative politics has emerged, it's time for us to recognize the deep changes that have taken place in our politics. Obama was wrong in 2004. The nation's democracy moved in a very combative and divisive direction that would not be reversed by a president who believed in a different style of governance. The forces that took hold in the Age of Obama were deeply entrenched and much bigger than any individual, including Trump.

Follow CNN Opinion Join us on Twitter and Facebook

While much of the nation's punditocracy likes to present Trump as some kind of anomaly or aberration, nothing could be further from the truth. A look back at the Obama years reveals, as the President would admit when his term was over, that we as a nation should have seen this coming.

In the following brief essays, some of the nation's top historians discuss and draw upon their contributions to my new book, " The Presidency of Barack Obama: A First Historical Assessment, " taking a look at some of the ways Obama did -- and did not -- change America.

The views expressed in the following contributions are solely those of the authors.

Kathryn Olmsted: Bush and Obama's counterterrorism policies were oddly similar

Kathryn Olmsted

Though his supporters thought he would bring new hope and wholesale change, Barack Obama shared President George W. Bush's core beliefs about terrorism and adopted remarkably similar policies. Obama generally preferred multilateral, negotiated solutions to foreign policy problems, but he made an exception when dealing with terrorists.

On many Tuesdays during his presidency, Obama convened an extraordinary meeting in the Oval Office. His national security aides would show him mug shots and short biographies of alleged terrorists. The suspects were Yemenis, Saudis, Afghans and sometimes Americans. They included men, women and even teenagers. The President would look over these chilling "baseball cards," as one aide called them, and pick which subjects should be put on a kill list, to be assassinated on his orders.

Sometimes these orders had broad public support, such as his decision to launch a raid that ended in the killing of Osama bin Laden in 2011. And sometimes they were more controversial, especially when civilians were inadvertently killed.

The decision by a liberal President -- a former professor of constitutional law -- to embrace an official program of targeted killing of suspected terrorists was one of the most surprising developments of the Obama presidency. Moreover, the assassination program was just one of several hardline Bush administration counterterrorism policies that Obama chose to continue.

Obama's counterterrorism policies did differ from those of Bush in one significant way: the new President was much more concerned that those policies should stay within US and international law. Obama decided to normalize his predecessor's practices and make them legal by tweaking the programs, or, if necessary, by changing the laws to fit the policies.

Kathryn Olmsted is professor of history at the University of California, Davis.

Eric Rauchway: Obama's economic policy delivered -- but too slowly

Eric Rauchway

Barack Obama's presidency was defined by the economic crisis he inherited. By the time he took office in January 2009, it was clear, as one of his advisers said, his "No. 1 priority was going to be preventing the biggest financial crisis of the last century from turning into the next Great Depression." Obama's economic policies did avert a collapse as severe as that of 1929. But they also left the nation struggling under a slow recovery.

Even before winning the election, Obama lobbied Congress to pass the Emergency Economic Stabilization Act, which became law with bipartisan support on October 3, 2008, and provided the secretary of the treasury with $700 billion to spend on relief for troubled financial institutions. These relief payments, better known as "bailouts," expanded beyond banks to encompass corporations like General Motors and Chryslers. The business failures thus prevented might well have been catastrophic.

The cross-party cooperation that enabled the bailouts did not survive Obama's inauguration. Economists of various ideological inclinations strongly supported a large economic stimulus to spur recovery, but Republicans in Congress declined to cooperate in crafting the stimulus as they had in the bailout. Moreover, White House officials also downplayed the need for a bold investment in recovery, reducing their request for a stimulus to a number well below what they believed necessary.

The result was a substantial fiscal stimulus, approximating $800 billion , that was nevertheless hundreds of billions of dollars too small to induce a proper recovery. And while, by the time Obama left office, the economy had largely recovered and unemployment had fallen substantially, it took far longer than it should have. A proper stimulus, unlike the bailouts, could have done much more to put money immediately into the hands of ordinary Americans. Its absence contributed to disillusionment with the institutions of representative government.

Eric Rauchway is the author of seven books, including the forthcoming "Winter War: Hoover, Roosevelt, and the First Clash over the New Deal" (Basic Books, 2018). He teaches history at the University of California, Davis.

Peniel Joseph: The racial paradox of Obama's presidency

Peniel Joseph

The most painful irony of the watershed presidency of Barack Obama is the fact that the nation's first black commander in chief proved unable to fundamentally transform the world's largest prison state, one that disproportionately warehouses African-American men and women. Glaring racial juxtapositions simmered during Obama's first term -- one that found black Americans hit hardest by the recession in terms of unemployment, homes lost and wealth vanished. But they exploded during Obama's second term, which was punctuated by urban rebellions in Ferguson, Missouri and Baltimore, Maryland, the rise of Black Lives Matter and waves of anger over a justice system that seemed intent on pushing impoverished African-Americans from elementary school to juvenile detention centers to prison cells.

The former-community-organizer-turned-President attempted to address criminal justice reform through the appointment of Eric Holder, the first black attorney general, who took major steps to have the federal government serve as a model on ending the nation's system of mass incarceration. Under the leadership of Holder and his successor, Loretta Lynch, the Department of Justice took both sweeping and incremental steps to curb the government's rate of incarceration of black bodies, making inroads on sentence reduction for nonviolent drug offenders, expanding prosecutorial discretion for minor drug crimes and increasing funding for rehabilitation and work programs, designed to reduce the nation's prison population.

In 2015, Obama became the first president to visit a federal prison, and vowed during a speech before the NAACP in Oklahoma to try and end mass incarceration. Yet Black Lives Matter activists, who personally met with Obama in the aftermath of Ferguson, expressed open frustration with the President's failure to meet the prison crisis with bolder words and action.

The Obama administration proved to be the most proactive in recent history in addressing criminal justice reform. Yet these efforts paled in comparison to the depth and breadth of a criminal justice system that BLM activists and others argued was a gateway to wider systems of racial and economic oppression that flourished, ironically, on the watch of the first black president.

And the Sentencing Reform and Corrections Act, a bipartisan Senate bill, that would have reduced mandatory minimum sentencing for nonviolent drug offenders, still failed. In the midst of the 2016 election year, in which Obama was now a lame duck president, neither the Senate nor the House took the time to bring a version of the bill for a full vote.

Peniel Joseph is the Barbara Jordan Chair in Ethics and Political Values and the founding director of the Center for the Study of Race and Democracy at the LBJ School of Public Affairs at the University of Texas at Austin, where he is also a professor of history. He is the author of several books, most recently " Stokely: A Life ."

Michael Kazin: Obama's presidency revived the left's energy

Michael Kazin

Many American leftists criticized Barack Obama for failing to govern as the transformative progressive his inspiring campaign had promised he would be. But the disappointment helped produce an ironic result. The left, defined by the birth of new social movements like Occupy Wall Street in 2011 and Black Lives Matter in 2013, grew in strength, spirit and creativity during the Obama years -- due, in no small part, to the gap between what most moderate Democrats and leftists had hoped his administration would accomplish and what actually took place.

Their frustrations helped fuel an upsurge of protest and organizing that propelled the issues of police killings of black men and economic inequality to the forefront of national politics. They also did much to make what became a heated, two-person battle within Obama's party to succeed him a contest to prove who could sound more progressive than the other.

Something like this had happened twice before in modern US political history. During the 1930s and 1960s, the left also thrived when liberal presidents were in office. There were, of course, significant differences between what occurred during Obama's presidency and those of Franklin D. Roosevelt, John F. Kennedy and Lyndon B. Johnson. Still, in all three eras, the left responded to reformist chief executives in similar ways. Intellectuals and organizers found their voice on issues they could use to build their movements both in numbers and confidence.

However, during those previous eras, leftists built institutions that sustained their activism and won signal victories that altered the politics and, to a degree, the culture of the nation. The left that began to thrive during the Obama presidency did not develop into such a mature, enduring force. And it is too early to know whether its spirited resistance against the Trump administration and Republican Party's dominance of the federal government will produce that result.

Jeremi Suri: Obama challenged the militarization of American foreign policy

Jeremi Suri

Barack Obama's election was possible because of a failed war in Iraq. The new President promised change in the way the country conducted itself overseas. He offered a liberal internationalist vision -- emphasizing multilateralism, negotiation and disarmament -- after eight years of aggressive militarism.

Obama sought to tame war with law and end American military conflicts that undermined the values of the nation. The early 20th century was a formative period for international law, when American leaders sought to build an international system governed by rules, consensus and arbitration. Obama pursued similar goals in his efforts to negotiate global reductions in nuclear weapons and carbon dioxide emissions, among other issues.

He reversed more than 55 years of Cuban-American conflict, turning a powerful source of anti-American hostility in the Western Hemisphere into an opportunity for newfound American trade and travel. Obama also negotiated and implemented an agreement with six other international signatories that halted Iranian nuclear weapons development for at least a decade.

The most obvious failure of Obama's foreign policy was in Russia. The eight years of his presidency witnessed the poisoning of what were still promising ties between the United States and Russia in 2008 -- and a return to Cold War hostilities. In Ukraine, Syria and even in our own presidential elections, the White House failed to deploy sufficient political and economic pressure to make Moscow abandon its aggressive tactics.

Obama will have enduring influence as one of the few US leaders since the Second World War to challenge the militarization of American foreign policy. He succeeded only in part, and his presidency triggered a dangerous backlash.

Jeremi Suri holds the Mack Brown Distinguished Chair for Leadership in Global Affairs at the University of Texas at Austin, where he is a professor of history and public affairs. Suri is the author and editor of nine books, most recently " The Impossible Presidency: The Rise and Fall of America's Highest Office ."

Meg Jacobs: Obama, the rugged environmentalist

Meg Jacobs

In one of his boldest moves, President Barack Obama came into office promising to protect this and future generations from the threat of global warming. After he lent tepid support to the Waxman-Markey bill, which would have set cap and trade regulations to limit fossil fuel emissions and been the most significant legislative environmental breakthrough since the 1970s, it fell apart in the Senate.

In the face of legislative obstacles, Obama turned to executive action. In August 2015, he announced his Clean Power Plan to cut the nation's carbon emissions from coal-fired power plants. In November 2015, Obama rejected the Keystone XL oil pipeline that would transport oil from the tar sands in Canada to the refineries in the Gulf of Mexico. In September 2016, he signed the Paris climate deal, acting unilaterally on an international agreement without submitting it to the Senate. Finally, Obama protected millions of acres of public lands and waters from development.

But the more Obama took deliberate action, the more he triggered greater resistance, especially after the rise of climate change deniers on the right. And a year after he left office, few of his environmental policies have stuck. Using executive action to tackle climate change made Obama a brave leader, including on the global stage.

However, his inability to get cap and trade legislation passed made his accomplishments vulnerable to reversal. And his use of executive orders enabled Trump to issues ones that reversed them quite easily.

His environmental legacy, much like his overall legacy, suggests that good policies are not worth much if they rest on bad politics. Obama's inability to change the political calculus in favor of green policy captures the larger failures of his presidency.

Gary Gerstle: America is still burdened by its racial past

Gary Gerstle

Barack Obama always understood how much racism had disfigured America. But he also believed, like Martin Luther King Jr., that America would one day deliver on its most inspiring proposition: namely, that all men are created equal and entitled to life, liberty and the pursuit of happiness. That an Obama presidency might catalyze a new age of racial equality explains the joy that rolled across America on election night 2008. Everywhere, one network reported, Obama supporters "danced in the streets, wept, lifted their voices in prayer." On January 20, 2009, 1.8 million Americans filled every space on the Washington mall to behold an event they never expected to see: the swearing-in of the country's first African-American president.

But as had happened so often in the past, this advance in racial equality became an occasion for mobilizing the forces of racial reaction. So-called "birthers" made the fantastical claim that Obama had not been born in the United States, and thus occupied the White House illegitimately. Anti-Obama artists delighted in depicting Obama as an African witch doctor or as a monkey, and thus as unfit to lead America. By 2015, nearly half of Republicans had convinced themselves that Obama was a Muslim who was leading the country to ruin. Donald Trump grasped the depths of this racial anxiety and used it to propel himself to the White House. Trump will not succeed in extinguishing Obama's legacy, but his presidency reminds us how much America is still burdened by its racial past.