It is easy to dismiss the “Come Together and Fight Back” Tour that this week will take Vermont Senator Bernie Sanders and Democratic National Committee chairman Tom Perez to eight cities in eight states this week as mere political theater. But this tour has the potential to finally begin redefining a Democratic Party that is still struggling with its identity after the disastrous 2014 and 2016 election cycles. That’s a big deal, not just for a party that lacks focus but for an American political process that will alter dramatically—for better or for worse—in the months and years to come.

Political parties change identities over time, as anyone who has watched the sorry trajectory of the Republican Party of Abraham Lincoln, Teddy Roosevelt, and Dwight Eisenhower can certainly attest. Sometimes, parties evolve. Sometimes, parties respond to moral and political demands that can no longer be denied. That was certainly the case for Democrats in the late 1940s and ’50s, when wise members of the party began to recognize the necessity of a clean break with the Southern segregationists who had historically been central figures in the Democratic coalition.

Though many Democrats still do not fully recognize the fact, their party is again at a moment where it must change.

The party of Franklin Roosevelt and Harry Truman began veering in the 1970s toward more centrist economic approaches. By the 1990s, it was swamped by so-called “Third Way” thinking that embraced free-trade fabulism, deregulation of banking and Wall Street, and the cruel lie that there can be some sort of “win-win” compromise between crony capitalism and the common good. It was never true that all Democrats favored centrist economics, but too many leaders constrained the party’s identity with a perceived need to keep on the right side of Wall Street.

Then came the 2016 primary race, which drew clear lines of distinction. The Sanders campaign, with its urgent advocacy for a $15-an-hour minimum wage, fair trade, single-payer health care, taxes on the rich, necessary regulation of big banks, and profound political reform, excited millions of voter—particularly frustrated Democrats, progressive independents, and, above all, the young voters who will decide whether the Democratic Party has a future. And although Sanders did not win the nomination, he won the debate. The party platform reflected his campaign’s progressive values. And Hillary Clinton embraced much of his agenda in her fall campaign.

Although Tom Perez did not back Sanders in 2016, he has a long track record of positioning himself on the left on labor rights and a host of other issues. That helped him when he faced off against a key Sanders backer, Representative Keith Ellison of Minnesota, in a closely contested race for DNC chair.

The Perez-Ellison race was often portrayed as a contest between the party establishment and the Sanders camp, but there was more to it than that. Many 2016 Clinton backers, including Senate Democratic leader Chuck Schumer and the heads of several major unions, supported Ellison in 2017. And Perez went out of his way to emphasize his belief that the party needed to change.

The party does need to change. It must become dramatically more militant on economic issues. Democrats cannot simply say “no” to Donald Trump; they must provide a clear and coherent progressive populist alternative to the “billionaire populism” of a president who never was—and never will be—committed to advancing the interests of workers, farmers, small business owners, students, and retirees.

Democrats must also provide a clear and coherent alternative to the “Third Way” politics that weakens the message, and the appeal, of their party. The era of the so-called “New Democrats” and the old DLC (officially the Democratic Leadership Council but, in reality, as Jesse Jackson explained, “Democrats for the Leisure Class”) must be finished—once and for all.

That is, however, easier said than done. Real change is hard. It must be conscious and it must take place in the open. That’s where the Sanders-Perez tour comes in.

The senator and the party chair are working together to send a clear signal about where the Democratic Party stands. That signal will have to get even clearer; but having Sanders and Perez on the same page is important.

They’re saying the right things, announcing that their tour will “speak out for raising the minimum wage to $15 an hour, pay equity for women, rebuilding our crumbling infrastructure, combating climate change, making public colleges and universities tuition-free, criminal justice reform, comprehensive immigration reform and tax reform which demands that the wealthy and large corporations start paying their fair share of taxes.”

And they’re traveling to the right places—Maine, Kentucky, Florida, Nevada, Utah, and Arizona—acknowledging the need for a 50-state strategy. They’re inviting the right people, including Ellison (who will appear midweek in Texas and Nebraska with Sanders) and Planned Parenthood Action Fund president Cecile Richards (who will close the week off with Sanders and Perez in Las Vegas).

No one should imagine that this is the end of a process, however. It is only a beginning. But it is the right beginning.

It matters that, in their joint statement announcing the tour, Sanders and Perez correctly assessed the challenging moment in which the party must define not just its agenda but its mission. “At a time of massive income and wealth inequality and a shrinking middle class, we need a government which represents all Americans, not just Wall Street, multinational corporations and the top 1 percent,” they said. “Regardless of where they live or their political affiliations, most people understand that it is absurd for Republicans in Congress to support huge tax breaks for billionaires while pushing for cuts to Social Security, Medicare, and Medicaid. They understand that the recent Republican health-care proposal that would have thrown 24 million Americans off of their health insurance, substantially raised premiums for older workers, and defunded Planned Parenthood while, at the same time, providing almost $300 billion in tax breaks to the top two percent is a disgraceful idea.”

Now Sanders and Perez and millions of grassroots Democrats must push forward. They must build a different Democratic Party. It cannot be a party that merely opposes Trump and Trumpism. What Sanders and Perez and Democratic activists must forge is a Democratic Party that, with its embrace of economic and social justice, can present itself as the absolute antithesis of Trump and Trumpism.