Currently, 34 states and D.C. allow voters to cast an absentee ballot for any reason, and millions of voters still have to queue up in person on Election Day — an activity that blatantly violates new federal guidance against gathering in groups of 10 or more people, as Ohio Gov. Mike DeWine pointed out Monday when calling for the postponement of his state's primary. While advocates have unsuccessfully called for the adoption of universal vote-by-mail for decades, they’re hoping the coronavirus pandemic serves as a wakeup call.

In a statement issued Tuesday following Maryland's decision, Democratic National Committee Chairman Tom Perez urged states to not further suspend primaries, but to embrace vote by mail.

"The DNC is urging the remaining primary states to use a variety of other critical mechanisms that will make voting easier and safer for voters and election officials alike. The simplest tool is vote by mail," Perez said. "States that have not yet held primary elections should focus on implementing the aforementioned measures to make it easier and safer for voters to exercise their constitutional right to vote, instead of moving primaries to later in the cycle when timing around the virus remains unpredictable.”

Perez, as chair of the DNC, has little sway over how individual states actually administer their elections.

Other states are already more prepared to handle the coronavirus outbreak because of their earlier adopting of mail voting. Kansas Democrats, which are holding are party-run primary this year, had already planned on sending out mail ballots to every registered Democrat in the state on March 30. The ballots, which also use ranked-choice voting, need to be postmarked by April 24 ahead of the May 2 primary.

“In the 15 years I’ve been pushing this, we’ve never had a public health and safety argument for this. Now, we do,” Sen. Ron Wyden (D-Ore.), the lead author of a federal vote-by-mail bill, told POLITICO. “Now, for states to say they don’t have a fallback plan and they’re just going to cancel or delay elections – that's not acceptable when we’re in the middle of the pandemic.”

Last week, Wyden introduced a retooled version of his decades-old bill targeted for situations like the coronavirus pandemic. He’s currently in the process of convincing fellow senators to support it, and pushing for it to be included in one of the upcoming relief packages Congress is currently putting together.

Under the legislation, if 25 percent of states declare a state of emergency, all states have to offer universal vote-by-mail for one election cycle, and the federal government will provide $500 million to make sure pre-paid, self-sealing envelopes are distributed so that voters aren’t spreading germs or having to pay out of pocket.

Even without a federal mandate, Wyden says, the move towards vote by mail is already accelerating in red and blue states alike.

“States are already moving in this direction because people are saying, ‘What other option is there?’” he said.

But even some proponents of mail balloting worry about a potential rapid switch to a predominantly mail-in system across the country.

“I do think there might be particular challenges to go from in-person voting to almost exclusively vote-by-mail systems,” Dale Ho, the director of the Voting Rights Project at the ACLU, said.

“Look, if a state can do it … it is probably due diligence at this point to explore the possibility. But that is a major, major change in the midst of an election year,” he added, voicing concern that such major change could potentially disenfranchise some, like low-income or Native American voters, who may not have a fixed address on file with the state.

Ho said that states should, at a minimum, adopt no-excuse absentee voting and make changes in the law to better accommodate voting by mail. Those changes include pushing back the deadline for when mail ballots must be received, allowing election officials to start processing ballots before Election Day, and providing federal funding to support state and local election administrators.

Marc Elias, the prominent Democratic election lawyer who also supports expanding mail balloting , said there also need to be changes to laws in some states that allow individual poll workers to toss out a mail-in ballot if they think the signature on the envelope doesn’t match the signature on file. Voters’ signatures can change over time, they argue, due to age or a disability.

“It's junk science,” said Elias, who is currently suing Michigan over its signature verification law. “At a minimum, voters need to be notified that someone doesn’t think their signature doesn’t match and given an opportunity to fix it.”

Maryland will likely not be the last state to postpone its primaries. Hogan said “other governors are expected to do” the same “later today, or the days ahead.” A spokesperson for Hogan tweeted that “we expect other Acela states to take similar steps.”

The April 28 primary was informally referred to as the Acela Primary, because the states voting that day are connected by the popular Amtrak line. Connecticut, Delaware, New York, Pennsylvania and Rhode Island are all scheduled to vote on April 28; none of them have modified their primaries as of yet.