Democrats and Republicans girded Wednesday for a legal showdown to decide the winner of the tight presidential race between Republican Donald Trump and Democrat Joe Biden.
After Trump declared he was ready to go to the US Supreme Court to dispute the vote counting, his campaign announced a recount demand in Wisconsin and lawsuits in Michigan and Pennsylvania, three states critical to winning the presidency.
US networks have called Michigan and Wisconsin for Biden, while Pennsylvania remains a tossup.
Late Wednesday the Trump campaign filed suit in a fourth battleground, Georgia, as the president's lead there shrank to less than a percentage point.
Trump's behaviour raised the spectre of the election ultimately being decided, as in 2000, by a Supreme Court ruling on how states can tally votes.
The Trump campaign lawsuits attack a unique aspect of the 2020 election — that millions of voters cast mail-in ballots because of the coronavirus pandemic.
The Covid-19 threat forced states to promote mailed ballots and change rules on how they would be collected, verified and tabulated.
That included extending the periods for receiving ballots, due to an overburdened US Postal Service, adding time for vote-counting.
The Republicans say some of those changes were decided or implemented improperly and in ways that favour Democrats.
In Pennsylvania the Trump campaign said it would join an existing Republican suit over the state's deadline extension for receiving mail-in ballots.
If successful, they have the potential to disqualify tens of thousands of ballots that arrived after November 3.
Extension was legal
The Pennsylvania Supreme Court ruled that the extension was legal, and last week the US Supreme Court declined to get involved.
But the high court left the door open for a post-election challenge.
Trump's campaign also said it was suing to have Pennsylvania ballot counting temporarily halted, alleging the process was being hidden by Democrats. In Philadelphia the counting was live-streamed.
And they sued over changes to voter identification — made to adjust to the pandemic — saying it violated the election code.
In Michigan, the Trump campaign sued to halt ballot counting saying they were not given "meaningful access."
The Georgia suit wants counties to "separate any and all late-arriving ballots from all legally cast ballots" that arrived by the 7pm Election Day deadline, Trump deputy campaign manager Justin Clark said.
Can courts decide the election?
In 2000 the White House contest between Republican George Bush and Democrat Al Gore rested on one state: Florida.
With Bush ahead by just 537 votes, and with problems with the state's punch-card ballots, the Gore campaign sought a state-wide recount.
The Bush campaign appealed the case to the US Supreme Court, which ruled to effectively block the full recount, handing Florida -- and the election -- to Bush.
Experts say such lawsuits are only practical if focused on a real problem and the vote gap is narrow.
If the margin separating candidates in that state is two or three percentage points — say, a 100,000 vote difference in Pennsylvania — "that's pretty difficult to be litigating at the end of the day," said Derek Muller, a law professor at the University of Iowa.
However, said Muller, "if it comes down to one state, then I would expect really serious litigation."
Skittish Supreme Court
If a campaign or candidate sues over state regulations, it has to first exhaust its options in the state justice system before heading to federal court and the US Supreme Court.
By piggybacking on the existing ballot extension case, the Trump campaign has raised its chances of reaching the high court.
But the Supreme Court has been cautious over involvement in voting matters that are decided by states, and is aware that it risked its standing as an independent body by effectively handing the 2000 election to Bush.
A case would put the political leanings of the court's six conservative and three liberal justices in the spotlight — especially on Amy Coney Barrett, who joined the court only last month.
Trump said he rushed her appointment in part so she could be in place to hear any election cases.
The Supreme Court felt like it needed to intervene in 2000, "but it's not necessarily clear they would feel the same way today," said Muller.