Editor's Note: (Julian Zelizer, a CNN political analyst, is a professor of history and public affairs at Princeton University. He is the author and editor of 24 books, including, "The Presidency of Donald J. Trump: A First Historical Assessment." Follow him on Twitter @julianzelizer. The views expressed in this commentary are his own. View more opinion on CNN.)
(CNN) Does Boris Johnson's downfall mark the end of an era? He and former President Donald Trump dominated the world stage over the past few years, pushing forward explosive policies that broke sharply with their nation's long-held core positions. For Johnson, his biggest legacy as prime minister will be his embrace of nationalism by enacting Brexit and breaking the United Kingdom away from the European Union. For Trump, it will be his privileging of an America First agenda and weakening ties with key allies while pushing domestic policy sharply to the right on issues such as immigration and climate change. And, of course, Trump's campaign to overturn the 2020 presidential election opened a new and dangerous door for anti-democratic forces within the US.
Beyond the letter of policy, both men shared a tumultuous approach toward governing. They appeared to move from one crisis to the next without a larger game plan, deploying chaos as a tool. Both were media-centered politicians who were willing to break with traditional norms. They played fast and loose with the facts, depending on disinformation as a political weapon. The cronyism and willingness to use power for self-interest revealed men who were willing to exploit vulnerabilities in their political systems to their maximum advantage.
So, what comes next? Will the conservative populism they championed outlast their tenures? Or do their falls from power mark the beginning of a new era in conservative politics?
Our moment bears some resemblance to the end of the 1980s, when the two most influential figures of conservatism -- US President Ronald Reagan and British Prime Minister Margaret Thatcher -- ended their tenures. For Reagan, that moment took place after the end of his second term in 1989, while Thatcher stepped down in 1990. Both figures had been extraordinarily influential, pushing a brand of conservatism that privileged the virtues of the market, blasted the role of government, attacked organized labor, and insisted on a hawkish approach toward foreign policy. Together, Reagan and Thatcher remade international politics by bringing legitimacy to a vision of politics that would have been deemed too radical just a few decades before they took on their leadership positions.
But their brand of conservatism never disappeared. The Republicans and the Conservative Party simply absorbed the basic principles that these figures had espoused and the legacy of their economic policies, including the primacy of deregulation, remain relevant.
What will happen today? The same is most likely. Both Trump and Johnson instituted profound changes in their parties that will be difficult to reverse. In the US, Trump's political future remains uncertain, but a number of other Republicans are stepping forward to promote what might be called Trumpism -- some would say it is just Republicanism in 2022 -- in more polished and politically viable ways. Florida Gov. Ron DeSantis is one prime example. In other words, the agenda of the Trump White House won't disappear. The only question is whether others will replace Trump as the voice of those policies.
We're probably going to see a similar scenario in the UK following Johnson's resignation. History shows that major changes, such as Brexit or Trump's Supreme Court coalition, are not easy to undo. And new leaders, often from the opposition party, may come into power, but they can't easily remake the existing political landscape.
It's also worth noting that both Trump, a former reality TV star, and Johnson, a former journalist, are the products of their times. Trump and Johnson were both skilled at exploiting attention, spouting untruths and delivering simple messaging that could cut through the firehose of information to position themselves as strong leaders. Trump had "build the wall," and "lock her up," while Johnson touted the slogan, "Get Brexit done." The context that gave rise to both leaders mattered. And that context won't change any time soon. What we're likely to see now are fellow party members taking a page from their playbooks and turning to comparable methods.
One notable difference is that in the United Kingdom, it appears the Conservative Party still has limits, even if those are based on pure political calculation. In the end, the party recognized that Johnson had gone too far and that it would be better off without him at the helm.
It's difficult to imagine a similar inter-party revolt could have taken place within the GOP during the Trump presidency. Instead, the Republican Party has shifted to a place where there are seemingly no guardrails, with nothing off limits. Just look at the alarming number of Republicans who have simply doubled down on Trump's election denialism, clamored for his endorsements and parroted his major positions.
Johnson and Trump might possibly be gone from the political stage, but their legacies will endure. Their form of conservatism will retain a deep hold on their respective parties and continue to influence politics well into the future.