An all-out war over mail voting has erupted in courts across the U.S. Here’s what’s at stake.

Legal battles will have an outsize impact on whose vote gets counted this year, and voting rights advocates fear new rules will perpetuate old problems.

USPS warning about mail-in ballots
USPS warning about mail-in ballots

NBC – Do you have to request an absentee ballot application, or will one be sent to you automatically? Will your ballot be counted if the mailman is late? If you fill out your absentee ballot wrong, can you fix it?

Questions like these — the fine print of democracy when it comes to mail voting — are at the heart of a record-breaking, high-dollar legal war being waged in courtrooms nationwide, fueled by the coronavirus that’s upended the idea of holding a presidential election as usual and by President Donald Trump’s constant warnings about widespread voter fraud that no one can prove exists.

"This is clearly a historic high," Trevor Potter, the former commissioner and chairman of the Federal Election Commission and now president of the Campaign Legal Center, a nonprofit watchdog, said of the sheer number of lawsuits tied to vote by mail. "It would have been a contentious fall without the pandemic, but the pandemic changes everything because it has caused so many states to revisit how they vote."

Substantive change to voter access in multiple states all at once is rare, but this year, officials have pushed to make mail voting easier to help protect people from the coronavirus. Plenty of these changes are happening in the courts — many state legislatures are out of session — as state officials, advocates and partisans duke it out over how to adapt existing election laws to fit a pandemic.

NBC News has reviewed more than 175 suits in 43 states and the District of Columbia contesting everything from whether postage must be prepaid on absentee ballots to where you can vote and how ballots can be legally transported from voters’ hands to election officials. It’s litigation that will decide who can vote in the 2020 presidential election and how, and advocates fear it will perpetuate and exacerbate racial biases that have long been baked into the voting system.

Democrats say they’re trying to make sure every vote counts, and voting rights advocates are raising the alarm that the expansion of existing absentee and mail voting systems could create widespread disenfranchisement and discrimination unless done correctly.

Republicans argue that last-minute election changes in the courts are improper and create opportunities for voter fraud and foreign interference, despite the fact that there is no evidence of widespread fraud and experts say foreign meddling in mail voting is extremely unlikely. The Republican National Committee (RNC) is litigating in 17 states, backed by a joint budget with the Trump campaign of $20 million earmarked for election-related legal fights and a small army of Election Day poll watchers and attorneys. The Republicans have repeatedly stepped in to defend against suits from advocacy and voting rights groups seeking to adapt election laws to pandemic realities. Justin Riemer, the RNC's chief counsel, told Axios that the legal work is "on steroids this year."

Much of voting rights advocates' litigation is aimed at lowering the absentee ballot rejection rates that have skyrocketed during the primaries.