The battle over voting rights in the US is a drama that's playing out in the Congress and state legislatures across the country.

In Philadelphia on Tuesday, Joe Biden gave a fiery speech, warning that American democracy is facing its greatest threat since the Civil War.

"There's an unfolding assault taking place in America today, an attempt to suppress and subvert the right to vote and fair and free elections," the president said.

Biden condemned recent efforts in 17 Republican-controlled states to pass laws curtailing when and where their citizens can vote - laws conservatives have framed as a response to allegations of voting fraud repeatedly made by Donald Trump in the months after his presidential defeat.

Many Republicans now believe the election was stolen from Trump - an assertion Biden called "the big lie" and one that has not been substantiated by concrete evidence.

Meanwhile, in Texas the fight over voting changes has led to drastic measures, as Democratic legislators have temporarily blocked passage of voting legislation by flying to Washington, DC. There, they are pressuring congressional Democrats to enact new federal rules for conducting elections that would supersede any state actions.

At the centre of this national debate is a question of what is the greatest threat to American democracy. Is it the security of an election process that in 2020 relied heavily on early and mail-in voting?

Or is it a system, corrupted by the influence of big donors and powerful interests, that makes voting more difficult than necessary, particularly for historically disadvantaged groups?

Democrats make their move

The Democratic effort at a national voting law centres around passage of the "For the People Act". It represents one of the most expansive federal reforms of the US election system in a generation.

The bill would guarantee that voters can receive a mail-in ballot if requested, mandate a minimum of 15 days of early voting before every federal election, require paper ballots and set standards for voting machines.

It would prohibit states from disenfranchising felons who have completed their sentences and enact new restrictions on undisclosed so-called "dark money" political contributions.

Many new voters would be automatically registered under the legislation, which also requires technology companies to disclose information about political advertising, create new government support for small donor-funded candidates and seek to end the practice of "gerrymandering" voting maps for partisan advantage.

In March the US House of Representatives approved the bill by a nearly party line vote, with one Democrat - Bennie Thompson of Mississippi - opposing because of concerns that the redistricting provision would disadvantage black voters.

Three months later, Republicans in the US Senate blocked passage of the For the People Act by use of the filibuster, a parliamentary procedure that requires 60 votes to pass major legislation. The bill only received 50 votes - all from Democrats in the evenly divided 100-seat chamber.

Democrats have since turned their focus to updating the Voting Rights Act, a 1960s-era law that has been curtailed by the US Supreme Court over the past decade.

Republicans dig in

As evidenced by the two congressional votes, Republican opposition to the Democratic legislation has been near complete.

House Minority Leader Kevin McCarthy called the bill an "unparalleled political grab" that would consolidate Democratic power.

"What this is really about is an effort for the federal government to take over the way we conduct elections in this country," Senate Minority Leader Mitch McConnell said shortly before his chamber blocked the bill. "It is a solution in search of a problem."

Former Vice-President Mike Pence, in one of his first public statements since being forced to evacuate the US Capitol after it was attacked by pro-Trump rioters, wrote in an opinion column that the Democratic proposal would "increase opportunities for election fraud, trample the First Amendment, further erode confidence in our elections and forever dilute the votes of legally qualified eligible voters".

A Trump-inspired state-level push

Behind the Democratic urgency in Congress to pass voting reforms is the reality that they're in a race with dozens of state legislatures enacting measures that curtail the same voting processes and systems that the For the People Act seeks to mandate.

Georgia, for instance, passed a law curtailing the use of drop boxes for ballot returns, requiring photo identification to vote by mail and ending early voting on Sundays, when many black churches - which tilt toward the Democrats - organise get-out-the-vote drives.

The move prompted protests and boycotts of the state, including the decision to move the Major League Baseball's July All-Star game from Atlanta to Denver, Colorado.

Other key political battlegrounds, including Florida, Arizona and Iowa, have enacted similar legislation.

In Texas, Democrats in the legislature left the state in July to deny Republicans a quorum and at least temporarily prevent passage of new voting measures that would limit mail-in balloting and curtail in-person voting hours and locations.

Republicans frame their laws as common-sense measures to protect against fraud and ensure that Americans have faith in the electoral process. Democrats counter that the confidence of the public has been damaged by the unsubstantiated allegations made by Trump and others after November's balloting.
A high-stakes fight

When it comes to a showdown between states and federal government over the rules of the election game, the US Constitution says the latter wins. That won't prevent a spate of lawsuits challenging the legality of the federal legislation if the congressional Democrats succeed in getting their bill passed by the Senate.

Just last month, the Supreme Court upheld an Arizona ban on the collection of mail-in ballots by third parties - an issue that would be directly addressed by the For the People Act.

Washington is no stranger to high-stakes political battles. Most sessions of Congress, particularly early in a new presidential administration, feature more than a few legislative showdowns touted for their potential long-term implications.

This one is a fight over how elections are conducted and - consequently - who is around to participate in all the other political battles to come.

The stakes don't get much higher than that.