Sen. Bernie Sanders (I-Vt.) sat down for an interview with The Washington Post on June 6 in Washington. (Kate Patterson for The Washington Post)

Wednesday’s We the People political summit at the Hyatt Regency, just blocks from the Capitol, was a glance into the Democratic Party’s future.

It wasn’t just that five potential marquee presidential candidates showed up — Sens. Bernie Sanders (I-Vt.), Elizabeth Warren (D-Mass.), Kirsten Gillibrand (D-N.Y.), Kamala D. Harris (D-Calif.) and Cory Booker (D-N.J.). Any of them could summon at least a dozen campaign reporters to a hotel ballroom.

More telling was who put the conference on: the Communications Workers of America (CWA), one of the few national unions that had endorsed Sanders for president in 2016. Teaming up with liberal groups like the Working Families Party, Demos, Indivisible and MoveOn, the CWA gave the five senators time to deliver a stump speech, then pushed them with questions from liberal activists.

Those questions were designed to push the 2020 hopefuls to the left, and they usually succeeded. When Gillibrand was onstage, a New York-based Indivisible activist asked whether the senator would “support a financial transaction tax that would discourage Wall Street excess and fund the kind of investments that would reduce inequality.”

Her answer was yes; it was the first time she had endorsed that idea, which had landed with a quiet thud when Sanders introduced it in 2015.

“I think income inequality is the greatest risk to our democracy that we have right now,” Gillibrand said. “In this economy today, we reward ownership. We don’t reward work.”

Two leading voices in the party, Sanders and Gillibrand, now favor a very small but lucrative tax on every form of Wall Street trade. When the Tax Policy Center looked at the proposal in 2015, it calculated revenue of $185 billion over 10 years. Democrats, put in a corner by the 2017 Republican-passed tax law, are increasingly talking up ideas like this. They would much rather be accused of holding stock traders upside down and shaking the change out of their pockets than of raising taxes on everyone.

So far, in the “invisible primary” that takes place years before candidates officially announce, the most talked-about potential candidates have been hard to find in early primary states. Local Democrats in Iowa and New Hampshire have been visited by Rep. John Delaney (D-Md.), who is already a candidate for president; by Los Angeles Mayor Eric Garcetti; by Rep. Tim Ryan (D-Ohio); and by voting rights advocate Jason Kander, who is addressing a New Hampshire party dinner this weekend.

But the debate about what the party stands for has been happening elsewhere. Wealthy potential candidates like Mark Cuban and Howard Schultz have laid out their policy positions in media interviews; a Schultz interview on CNBC, in which he urged Democrats to debate Social Security and Medicare cuts, got enough attention that Sanders was asked to respond to it. (Sanders called Schultz’s stance on health care and government spending “dead wrong.”) Liberal groups have offered up day-long forums for candidates to lay out policies, such as last month’s Ideas Summit organized by the Center for American Progress.

The We the People summit went further, with attendees knowing up front that they might get critical questions from the audience, in a room so full that it threatened to pass capacity. Booker, who still takes heat from activists over his vote against a Sanders-backed pharma bill, used a story about a Newark mentor to discuss racial injustice and economic inequality.

“Other countries are surpassing us, lifting people out of poverty, while our poverty rates are stuck,” he said. In a blink-and-you-miss-it moment, he called marijuana use “something the last three presidents did” — one way that Booker portrays other Democrats as latecomers to the cause of ending the drug war.

Sanders, with the least to prove to activists, mostly recapped his 2016 platform and remarked on how what had been called “radical ideas” were now in the Democratic mainstream.

“All these people around the country, they were saying: You’re nuts! You’re crazy!” he said, discussing the $15 minimum wage, universal Medicare and tuition-free public college. But activists were not successful in getting him to agree to defund Immigration and Customs Enforcement, a growing cause on the left, thanks to stories about ICE rounding up undocumented immigrants many miles from the border.

Warren, also on very friendly territory, used her time to indict the Trump administration and build a framework for criticizing it — “corruption.” Warren walked the audience through the connections between President Trump’s judicial nominees and the conservative donor network, and tied the scandals around Trump Cabinet nominees to Trump’s own governing philosophy.

“[It’s] corruption when Cabinet officials, when agency heads, and yes, when the president of the United States himself have deep conflicts of interest, and make themselves rich, and working people suffer,” said Warren, who urged Democrats to “hose out this cesspool.”

Harris, who is newer to the national activist circuit, made the same basic points as the other senators. When she differed, it was largely on style ground — she eschewed the personal storytelling of Booker and Warren, and described how she’d become a “joyful warrior,” fighting the administration while focusing on the day when Americans could come together to undo its work.

“Don’t let anybody take our flag,” Harris said. “When we march and we shout and we fight, this is a fight that is born out of love of country.”