Now that Democrats control both chambers of Congress and the White House, advocates of making Washington, D.C., the 51st state believe they are on the brink of a historic opportunity.

House Democrats passed the Washington, D.C. Admission Act on Thursday by a vote of 216 to 208, along party lines.

But D.C. statehood still faces a number of high hurdles, not only in the narrowly divided Senate but in public opinion. A 2019 Gallup poll found that nearly two-thirds of Americans opposed D.C. statehood. Last year, statehood advocates launched a campaign to introduce the nation to everyday residents of their country’s capital, arguing that perhaps the nation doesn’t know enough about the people who live in the District to have an informed position about making it a state. Since then, the cause has been increasingly embraced by liberal Democrats, many of whom see it as a basic civil rights issue

As the statehood bill moves to the Senate, here are the challenges that remain.

Why isn’t D.C. already a state? What does the Constitution say?

D.C.’s founding is enshrined in the Constitution, which provides that the District — “not exceeding 10 Miles square” — would “become the Seat of the Government of the United States.” For a brief period after the city’s creation in 1790, residents enjoyed voting rights and were allowed to cast ballots as residents of Maryland or Virginia. But those rights ended shortly after Congress moved into town and the new Capitol in 1800 and passed the District of Columbia Organic Act of 1801. The act stripped D.C. residents of their rights to vote in all federal elections, including for president, and gave Congress oversight of the city.

The District was not afforded presidential electors until the ratification of the 23rd Amendment in 1961; its residents didn’t get a nonvoting delegate in the House until 1970.

How can Congress change this?

Those opposed to making D.C. a state have argued that statehood for D.C. can’t happen without a constitutional amendment. They say the founders intended the entire District to serve as the seat of the federal government, not as a state. But legislation put forth by nonvoting Del. Eleanor Holmes Norton (D) would not eliminate the “seat of government” that the Constitution calls for. Instead, H.R. 51 would shrink the national capital to a small complex of federal buildings, while allowing the rest of the District to become a state.

Proponents of statehood argue that this plan preserves the federal enclave — whose only requirement is that it can’t exceed 10 miles square — and escapes the need for a constitutional amendment.

Outstanding questions remain over what would happen to the three electoral college votes currently afforded to the District when it becomes a smaller federal enclave. Democrats and Republicans agree the 23rd Amendment should be repealed so that the few residents of the federal enclave — namely, those residing at 1600 Pennsylvania Avenue — don’t retain them. But Republicans argue this needs to be done before statehood passes, essentially conditioning statehood on the amendment’s repeal.

What needs to happen for D.C. to become a state?

Now that statehood has cleared the House, it now faces a number of obstacles in the Senate.

Democrats occupy half the seats in that chamber, thanks to the January victories of Jon Ossoff and Raphael G. Warnock of Georgia, both of whom support statehood. That creates a 50-50 split in the Senate among Democrats and Republicans, with Vice President Harris able to cast the tiebreaking vote. She, like Biden, supports statehood.

But because of the Senate filibuster — which requires 60 votes rather than 51 for legislation to pass — a simple majority of Democrats in the Senate isn’t good enough to pass statehood; the bill would need the support of at least 10 Senate Republicans as well.

Alternatively, the Senate could vote to end the filibuster, meaning that 50 votes in favor of statehood — plus Harris as the tiebreaker — would suffice.

A number of senators are pushing various filibuster reform proposals, such as returning to the “talking filibuster,” or even creating an exception for voting rights legislation to counter Republican efforts to restrict voting access across the country.

Statehood advocates have another potential roadblock: Not all Senate Democrats have voiced support for D.C. statehood. Sens. Joe Manchin III (D-W.Va.), Angus King (I-Me.) and Mark Kelly and Kyrsten Sinema of Arizona have yet to state their positions. And not all of them support eliminating the Senate filibuster, including Manchin and Sinema.

What would the state be called?

The federal district would be reduced to a two-square-mile enclave, including the White House, Capitol Hill, the Supreme Court and other federal buildings. The rest of what is now the District would become the State of Washington, Douglass Commonwealth — honoring abolitionist Frederick Douglass.

Why statehood? Why not become a part of Maryland or Virginia?

While some have argued D.C. is too small to be a state, it’s more populous than Wyoming and Vermont, with 689,545 residents, according to U.S. Census Bureau data released April 26.

Statehood advocates say it’s a moral issue, an unjust lack of voting representation based on where a person lives — in this case, a historically African American city where 46 percent of residents are Black. Democrats are framing statehood as a central part of their voting rights platform.

But politically, Democrats also support the fight for statehood because D.C. would almost certainly elect two Democratic senators, making it easier for the party to solidify control of the Senate long-term. Local advocates avoid framing the debate as a partisan issue, saying it’s a question of equal representation under the law.

Still, Republicans are loath to give Democrats any political advantage. Some have instead pushed to make D.C. part of Virginia or Maryland, a proposal Rep. H. Morgan Griffith (R-Va.) put forth as recently as last fall; it did not go anywhere. Rep. Andy Harris, the only Republican in Maryland’s congressional delegation and a longtime opponent to D.C. autonomy, also supports the retrocession proposal. But most Marylanders oppose adding the District as a new county to their state, according to a 2019 Washington Post-University of Maryland poll.

Mayor Muriel E. Bowser (D) has been asked before about the possibility of retrocession. She has said D.C. would completely upend the current geopolitical powers in Maryland if it became a part of the state again. The District already has a larger population than any city in Maryland, though it is smaller than Montgomery and Prince George’s counties. Back in 2019, Bowser said retrocession would just mean the theoretical next governor of Maryland would probably come from the District.

In January, after a mob stormed the U.S. Capitol, Bowser told reporters the unprecedented assault added urgency to the cause for statehood: D.C. residents, she said, risked their lives to defend a Congress that affords them no voting representation.

With Democrats in control of the White House and both chambers of Congress, activists say they are in their strongest position yet to make D.C. the 51st state. (Drea Cornejo, Amber Ferguson, Daron Taylor/The Washington Post)

What is the argument against D.C. becoming a state?

Strict constitutionalists say that D.C. statehood goes against the intent of the nation’s founders. They argue the framers would have never wanted a small federal jurisdiction surrounded by a single state, which is the current solution prescribed by statehood advocates. They also raise the electoral-vote issue.

Republicans overwhelmingly agree that the only viable path toward statehood is through a constitutional amendment. Some in the GOP have also said that the District, and the people who live there, aren’t the same as the average American in other parts of the country. Republicans have argued the city is too corrupt and too financially dependent on the federal government to be the 51st state — although the former argument does not have any bearing on voting rights elsewhere in the country, and D.C. residents pay among the most federal income taxes per capita in the nation.

Last year, Sen. Tom Cotton (R-Ark.) said that Washington, as a state, would only be “an appendage of the federal government” where the only “vital industries” are lobbying and bureaucracy. Wyoming may have a smaller population than D.C., but Cotton said it has a greater right to statehood because it’s a “well-rounded, working-class state” with workers in mining, logging and construction.

And then there’s the endless battle to control the Senate Minority Leader Mitch McConnell (R-Ky.) has said that the campaign for statehood is just an attempt by Democrats to consolidate power with “two more liberal senators.” McConnell once called the Democrat’s campaign for statehood “full-bore socialism.”

How many times has the House voted on D.C. statehood?

Three times. The House first voted on D.C. statehood in 1993, but the bill failed, 277 to 153. Then, last June, the House passed legislation to declare D.C. the nation’s 51st state largely along party lines. It was the first time a chamber of Congress approved a bill granting the District statehood. The bill passed 216 to 208 on April 22, 2021. Every Democrat who cast a ballot voted for the bill; every Republican voted against.

The Senate has never voted on D.C. statehood, nor has a Senate committee. McConnell refused to bring the House legislation to a vote, but Schumer has pledged to try to move the legislation. Supporters are hoping for a Senate committee hearing in coming weeks.

Fenit Nirappil contributed to this report, which has been updated with new information.