Voting rights groups and the head of the Democratic National Committee want the states with remaining primary elections to offer voting by mail as a way to ensure that voters can safely cast their ballots amid the coronavirus outbreak.

A quick and easy fix? Not always.

For states that don’t already have vote-by-mail or that greatly restrict it, such a change could require amending state law. It also would require major changes to state and county voting and tabulating systems. Buying the equipment and software to track ballots and read the signatures on them could cost millions. And that’s not to mention deciding who pays for return postage — individual voters or taxpayers?

So far this year, one state has moved quickly to mail ballots statewide for the November general election. The top election official in Arizona, where about 80% of voting is already by mail, asked the Legislature on Wednesday to give counties permission to mail ballots to all registered voters.

Other states are being more limited in scope: Maryland postponed its primary but decided to hold next month's special congressional election by mail. On Wednesday, West Virginia election officials said they would make fear of getting the coronavirus a valid excuse for getting an absentee ballot for its May 12 primary. And the Democratic Party in Wyoming, which already was sending all its members ballots, has canceled the in-person portion of its presidential caucus.

As in Wyoming, the Democratic caucuses and primaries in Alaska, Hawaii and Kansas were already to be held largely by mail this spring. So far, none of the states postponing their primaries — Alabama, Georgia, Kentucky, Louisiana, Maryland or Ohio — has said they will mail ballots statewide.

A bill in Louisiana seeking to expand vote-by-mail was introduced even before the state's primary was pushed back, but it hasn’t received a legislative hearing and is opposed by the state’s top elections official. Pennsylvania lawmakers eased absentee ballot rules last year, and now Democrats want to expand voting by mail. Republicans, who control the statehouse, have generally resisted voting changes, and it’s unclear if the virus crisis is enough to overcome concerns about the costs of greatly expanding vote-by-mail.

In the absence of official action, some political and voting rights groups are vowing legal challenges. On Wednesday, the Democratic National Committee and Wisconsin Democratic Party filed a lawsuit seeking to force the state to extend the deadline to register to vote online or by mail, as well as ease some ID requirements for voter registration and absentee ballot applications. The suit also asks for mail ballots to be counted if they are received up to 10 days after the election as long as they are postmarked by Election Day.

Also Wednesday voting rights advocacy group Common Cause called for states to suspend in-person voting at least for the next few weeks. The group previously recommended expanded vote-by-mail access.

Opposition isn't unusual, typically because lawmakers or election officials believe it opens a pathway to voter fraud. The ability to receive a ballot in the mail is greatly restricted in 16 states.

Those states allow absentee ballots only for voters who give a valid reason to get one — and require they be requested for each election. Of those, Delaware and New York are phasing in no-excuse mail voting.

The hurdles to implementing voting by mail for all voters is why states might be better off taking only small steps at first, said Charles Stewart, a professor of political science at the Massachusetts Institute of Technology. That could mean simply making absentee ballots easier to get.

“Hastily implemented changes to voting rules and laws can end up causing all types of problems that you didn’t anticipate,” he said.

Doug Jones, an election security expert at the University of Iowa, said universal mail voting also raises concerns about voters illegally selling blank ballots or being coerced to vote a certain way.

On Tuesday, after Ohio postponed its primary and poll workers failed to show up at some Florida and Illinois precincts, Democratic National Committee Chairman Tom Perez called a shift to voting largely by mail “the simplest tool” to balance health concerns and the need to carry out a fundamental function of democracy.

A half-dozen states already have or are implementing systems where all voters are mailed ballots. They can mail them back, drop them off at designated spots or choose to vote in person on Election Day.

Oregon has been conducting elections that way since the 1990s. Since then, California, Colorado, Hawaii, Utah and Washington have implemented or begun phasing in similar systems.

With the coronavirus pandemic, the idea has generated more interest. The National Vote at Home Institute advocates for a switch to a mail-based voting system and consults with governments about it.

Said chief executive Amber McReynolds: “It’s better than hoping people show up and aren’t scared, and hoping that you don’t have a giant poll worker shortage and hoping polling places aren’t closed.”

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Mulvihill reported from Cherry Hill, New Jersey.

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Associated Press writers Frank Bajak in Boston; Melinda Deslatte in Baton Rouge, Louisiana; and Mark Scolforo in Harrisburg, Pennsylvania, contributed to this report.