Democratic presidential primary candidates jostled for the support of liberal activists from across the country on Monday as they were grilled on their commitment to political, economic, and social reforms.

Sens. Cory Booker of New Jersey, Kirsten Gillibrand of New York, Amy Klobuchar of Minnesota, Bernie Sanders of Vermont, and Elizabeth Warren of Massachusetts joined Washington Gov. Jay Inslee, Obama-era housing secretary Julian Castro, and former Rep. Beto O'Rourke of Texas in facing a litmus test on democratic principles at the We The People summit before about 1,000 activists who could become crucial in galvanizing a grassroots movement behind their respective White House campaigns.

Hosted by the Center for Popular Democracy Action, Communications Workers of America, Planned Parenthood Action Fund, Service Employees International Union, 32BJ SEIU, and the Sierra Club for their members, the presidential hopefuls were pressed on voting rights, representation, and the influence of money in politics. The Supreme Court was also a focus of the discussion after recent confirmation battles with Senate Republicans and decisions affecting workers' rights.

Several of the candidates borrowed from their stump speeches or spoke about a constitutional amendment enshrining the right to vote, abolishing the Electoral College, and rejecting donations from corporate political action committees, issues that have already been hashed out on the trail. Others proposed a raft of changes in an effort to stand out from the crowded primary field.

Here are four suggestions raised on Monday that have been little-explored so far in the 2020 race:

Reforming the Supreme Court, rather than "packing" the bench

Unlike other presidential prospects, Sanders said he was against increasing the number of seats on the Supreme Court. But he could support refinements to the system where there were term limits and justices on the bench were rotated with judges on the federal appeals court to infuse the institution with "new blood."

“My worry is that the next time the Republicans are in power, they will do the same thing, so I think that is not the ultimate solution," he said, earning applause when he mentioned his platform plank of declaring Election Day a national holiday.

Expanding the Freedom of Information Act to cover Congress

Castro pushed for federal lawmakers to be covered by Freedom of Information Act provisions. As it stands now, the legislative and judicial branches are absolved from the disclosure requirements, as are state and local governments.

"We have to make Congress subject to the Freedom of Information Act. We need to shine a light on what happens in Congress," he said while advocating for a boost in the minimum wage to $15 an hour and touting how his aides are allowed to unionize.

Introducing a constitutional amendment on campaign finance

O'Rourke, who used Monday's event as a platform to announce he would sign an executive order mandating that his hypothetical Cabinet hold monthly town halls, indicated his openness to constitutional revisions to counter the repercussions of controversial Supreme Court case Citizens United v. Federal Election Commission.

"If we need a constitutional amendment to show that corporations are not people, and money is not speech, and corporations cannot spend unlimited amounts, then so be it," he said.

Getting behind statehood for the District of Columbia

For Klobuchar, granting the District of Columbia statehood would be among her priorities for her first 100 days in office should she clinch the party's nomination and win the general election, along with comprehensive immigration reform, legislation taking on so-called "Big Pharma," and creating a public option within the country's healthcare system.

"I am proud to support statehood for Washington, D.C.,” she told attendees, adding it was "crazy" that many states refused to reverse steps that disenfranchise prisoners even after their release.