Wisconsin voters braving lines in face masks — after a last-minute Supreme Court ruling against extending the absentee deadline — could foreshadow a nationwide legal struggle over how to conduct elections during the coronavirus outbreak, election experts say.

Why it matters: "It's a harbinger of what's to come in the next skirmishes in the voting wars" from now through November, Richard Hasen, a professor and national election law expert at the University of California, Irvine, told Axios.

Wisconsin's breakdown showed how easily states' election law battles — already marked by bitter clashes over voting rights — can be supercharged by the virus.

When asked about Wisconsin on Tuesday, President Trump discouraged mail-in voting and cast doubt on its reliability. He called it “very dangerous,” “corrupt” and a mechanism for cheating.

By the numbers: Twenty-one states and Washington, D.C. still have presidential primary deadlines between now and June 23.

Fourteen have already postponed in-person elections or extended mail-in voting deadlines because of COVID-19, according to the National Conference of State Legislatures.

already postponed in-person elections or extended mail-in voting deadlines because of COVID-19, according to the National Conference of State Legislatures. Many could face similar challenges over decisions on election procedures or deadlines as coronavirus spreads.

Georgia, for example, has a primary on May 19. But poll workers are quitting and precincts have shut down, according to the Atlanta Journal-Constitution.

Wisconsin Gov. Tony Evers' last-minute decision to extend the mail-in ballot deadline complicated the situation. Election law experts hope most states will avoid that mistake, and start rolling out new policies and procedures well in advance.

What to watch: 2018 was a record year for election-related litigation, and Hasen expects 2020 to surpass it.

The Democratic National Committee has filed lawsuits in Georgia, Arizona and Texas because the states list Republican candidates first on general election ballots, something Democrats claim gives Republicans an unfair advantage. They've also sued over Kansas' delay in implementing a new law that would allow easier access to ballots.

The Republican National Committee is assisting New Mexico's state party to stop a lawsuit calling for an all vote-by-mail election, according to the RNC's Mandi Merritt. The RNC is also defending state election laws in Minnesota and Michigan.

The RNC is also defending state election laws in Minnesota and Michigan. Both parties have been involved in election-related legal fights in Wisconsin.

Another factor in the Wisconsin mess was divided government, with the Republican-controlled legislature shutting down Evers' attempt to postpone the Tuesday primary.

Other states with split political control could face similarly heated battles over election processes, Joe Sandler, a D.C.-based election and campaign finance lawyer, told Axios.

In addition to Wisconsin, North Carolina, Pennsylvania, Kansas, Montana, Michigan, Kentucky and Louisiana have Democratic governors but Republican-controlled state legislatures.

Maryland, Vermont, Massachusetts and New Hampshire have a Republican governor and a Democratic-controlled state legislature.

What they're saying: Partisan fighting and finger-pointing over long-debated election reforms has flared up as the coronavirus forces some states to consider alternatives to in-person voting.

Republican National Committee chairwoman Ronna McDaniel published an op-ed on Monday charging that "Democrats’ all-mail ballots proposal is a ruse to legalize ballot harvesting nationwide."

"What the RNC is doing — and they've made it very, very clear — over the course of the entire cycle is an orchestrated campaign of voter suppression, and the DNC is fighting back," the DNC's David Bergstein told Axios.

Go deeper:

The race to change how America votes