Sen. Elizabeth Warren (D-Mass.) in Cambridge, Mass., on Monday after announcing her plans to form an exploratory committee for a potential presidential run in 2020. (Scott Eisen/Getty Images)
Opinions editor

With apologies to Rep. John Delaney (D-Md.) and former housing and urban development secretary Julián Castro, Sen. Elizabeth Warren (D-Mass.) on Monday became the first major contender to enter the 2020 Democratic primary. Warren announced an exploratory committee with a five-minute video that was part biography, part diagnosis of what’s ailing average Americans. With such a large potential field, it is anyone’s guess how Warren’s presidential bid will go. But her entry is an unabashedly good development for Democrats.

As her announcement video shows, Warren has a very specific case underlying her candidacy. “America’s middle class is under attack,” she says, “How did we get here? Billionaires and big corporations decided they wanted more of the pie. And they enlisted politicians to cut them a bigger slice.” Inequality, she argues, is rotting our country.

Warren offers specific solutions as well. As The Post’s Jeff Stein outlines, Her Accountable Capitalism Act would mandate that large companies' boards be at least 40 percent controlled by workers. The idea is to reroute trillions of corporate income to laborers, whose pay has stagnated in recent‘‘ decades even as productivity has risen. Warren says she would crack down on the monopoly power of technology companies such as Apple, Google and Amazon. (Amazon’s founder and chief executive, Jeffrey P. Bezos, also owns The Post.) She supports a $15 minimum wage, as well as the Medicare-for-all plan of Sen. Bernie Sanders (I-Vt.).

There are other politicians who may compete with Warren in this ideological space. Sen. Sherrod Brown (Ohio) will likely overlap heavily with Warren; other senators such as Kamala D. Harris (Calif.) could as well, depending on how progressive they run. And then there’s Sanders: On the surface, the two may seem similar, but their approaches differ. Warren, broadly speaking, wants to make market systems fairer, while Sanders often wants to junk those systems altogether. As David Dayen wrote for the New Republic in October, “There’s a long gap between re-writing the rules of the game, as Warren wants, and turning over all the chess pieces, as Sanders does.”

But Warren and Sanders both support Medicare-for-all. They both oppose monopolies. They both back postal banking and breaking up big banks. In the end, the more voices sounding the alarm about inequality, the better. Furthermore, Democratic activists who have remained hostile toward Sanders since the 2016 primary might be more open to Warren and others' views. A strikingly large share of the party establishment, for example, has already come around to Medicare-for-all.

Warren, like every potential candidate, has her flaws. But her candidacy ensures that inequality will be a central issue in the Democratic primary. That is good news for the country.

Read more:

Who isn’t running for the Democratic presidential nomination?

An early tip sheet for 2020 Democrats

Elizabeth Warren jumps in first