Millions of demonstrators across the U.S. will take to the streets Saturday to call for action from Congress to prevent gun violence.

City officials in Washington, D.C., where the main March For Our Lives event kicks off at noon, estimate the rally will attract roughly 500,000 visitors to Pennsylvania Avenue.

It’s one of more than 800 such student-led marches taking place across the U.S. on Saturday.

Dozens of students from Marjory Stoneman Douglas High School in Parkland, Florida, where a gunman shot and killed 17 people in February, will lead the rally in Washington. They’ll be walking alongside pop stars Ariana Grande, Miley Cyrus, and Demi Lovato, and hundreds of thousands of young people from the D.C. area and across the country.

The Parkland students, who have spent over a month organizing the nationwide marches with the gun control advocacy group Everytown for Gun Safety, arrived Friday to meet with lawmakers on Capitol Hill and to discuss their experiences during the shooting at an event at the Newseum in downtown Washington.

“This trip is showing the politicians the true meaning of democracy,” Stoneman Douglas student Demitri Hoth told CNN on Friday. “They are not there to serve groups; they are there to serve people. It’s time for us to take control and be heard.”

Watch: Sights and Sounds From #NationalWalkoutDay Protest on Hill

Progress in Congress?

Congress has made some progress on gun legislation, especially in the 2018 omnibus spending package it passed early Friday morning, Republican leaders have said.

Senate Majority Whip John Cornyn of Texas and Democratic Sen. Christopher S. Murphy of Connecticut managed to add their bill strengthening the current federal background check system — the “Fix NICS Act” — to the omnibus.

The measure aims to hold federal agencies accountable for uploading information to the National Instant Criminal Background Check System, or NICS, and provides monetary incentives for states to comply with the federal plan.

Lawmakers began drafting the bill in November in the wake of the church shooting in Sutherland Springs, Texas, where an Air Force veteran killed more than two dozen people. The Air Force failed to upload a domestic abuse charge against the shooter to the NICS system, which would have barred him from purchasing the rifle he used at the church.

“After the tragedy in Sutherland Springs, I vowed to that community to do what I could so no family, school, or congregation would have to go through that again,” Cornyn said in a statement Friday. “While it’s not the only solution, I’m confident this bill will save lives.”

Both parties also agreed to provide funding for grants to schools to implement safety training and protocols, as outlined in the “STOP School Violence Act” the House passed last week.

And the omnibus included language that clarifies the Dickey Amendment, which Democrats say previously prevented the government from researching gun violence.

Democrats want more

But the buck doesn’t stop there, Democrats have said.

There is “a hope by the [Republican] majorities in both houses that, ‘If we put this in, can we say that we’re done [on gun legislation]?’” Sen. Tim Kaine told gun control advocates Friday at a roundtable discussion in Arlington, Virginia.

Democratic lawmakers still have a host of policy proposals to combat gun violence, including enacting a universal background check system and raising the minimum age to buy an assault rifle to 21.

Some of those proposals are nonstarters in a GOP-controlled Congress. Democrats, Kaine said, will be looking for gun measures their Republican counterparts find “palatable.”

“Rather than just bang our head against the ones that we think we’ll lose on,” the Virginia Democrat said, “we do have to strategize about the ones where we think we have some chance.”

Whether or not the March for Our Lives moves the needle on gun legislation, some Democratic lawmakers say the rally has already affected Republican plans on other legislative matters, including the rushed timeline on the omnibus passage.

House Minority Leader Nancy Pelosi accused her GOP counterparts of scrambling to “get out of town before the March for Our Lives.”

“That’s what I heard about the Republicans — they just don’t want to be around when the young people come to town,” the California Democrat said Thursday on the House floor.

Getting registered

After the Parkland shooting, some of the country’s top gun control groups — Everytown for Gun Safety and former Arizona Democratic Rep. Gabrielle Giffords’ Courage to Fight Gun Violence — announced they would work to register high school students nationwide to vote, or to pre-register those not yet 18 in states that allow such action.

Billionaire liberal donor Tom Steyer’s NextGen America will fan staffers and volunteers out to marches in nine different states Saturday for registration drives.

In 2018, for the first time, millennials have eclipsed baby boomers as the largest eligible voting bloc in the country.

How to get there

In D.C., the Metro is rolling out its ramped-up rush-hour service throughout the day Saturday and keeping “hundreds” of additional staff on hand to assist the hundreds of thousands of participants expected.

Starting at 7 a.m., trains will run every eight minutes on each of Metro’s six rail lines. Metro will operate additional trains on the Red Line between the Grosvenor and Silver Spring stops. If you’re riding on the Blue, Orange, or Silver lines, get off at Metro Center Station, which is two blocks north of Pennsylvania Avenue. Federal Triangle Station will be closed.

Officials have advised marchers to buy their SmarTrip cards Friday to avoid long lines at the automated kiosks on Saturday. Riders can pick up SmarTrip cards at CVS pharmacies and Giant Food stores.