US election 2020: What legal challenges is Trump planning?

Democrat Joe Biden has been declared president-elect, but President Donald Trump is challenging the result, alleging electoral fraud.

The Trump campaign - yet to provide any strong evidence of fraud - is pursuing lawsuits in several key states.

The individual states would usually handle any such lawsuits, but US attorney general William Barr has allowed federal prosecutors to probe the allegations.

Here's what we know so far.

Mr Biden is projected to have won here.

On 4 November, the Trump campaign filed a lawsuit alleging a lack of access for poll watchers in the state.

Poll watchers are people who observe the counting of votes, with the aim of ensuring transparency. They are allowed in most states as long as they are registered before election day.

In some areas this year, there were restrictions put in place before election day, in part due to coronavirus. There were also capacity limits set to avoid intimidation.

A 20-foot (six-metre) perimeter was set in the Philadelphia counting facility but this was challenged, and a court ruling on 5 November said it should be reduced to six feet - as long as poll watchers adhered to Covid-19 protocols.

On the same day, the Trump campaign accused election officials of violating the judge's order, and filed a federal lawsuit to stop the count in Philadelphia, which was rejected.

Rudy Giuliani, a lawyer for the president, said: "Even when a court order was obtained to allow the Republican inspectors to get six feet closer, they moved the people counting the ballots six further feet away."

Election officials insist they behaved properly, and have appealed to the state's Supreme Court.

The legal challenge in Pennsylvania also centres on the state's decision to count ballots that are postmarked by election day but arrive up to three days later.

On 6 November, Republicans appealed this ruling, wanting all postal ballots received after election day to be disqualified.

Matthew Weil, director of the Bipartisan Policy Research Center's elections project, says he is most concerned about this dispute as the nation's top court - the US Supreme Court - was deadlocked on it before the election.

This was before Justice Amy Coney Barrett, appointed by President Trump, was confirmed.

"I do think there is a risk that some of those [postal] ballots that were cast by election day and not received until Friday may be discarded", he said.

But Mr Weil added: "My guess is that it's not going to be a huge number of ballots that could be thrown out," so the election would have to be "very, very close for that to matter".

Another ongoing case disputes how long voters should be given to provide proof of identification if it was missing or unclear on their postal ballots.

Voters are currently allowed to do this up to 12 November, but the Trump campaign filed a lawsuit on 5 November seeking to reduce this deadline by three days.

On 9 November, the Trump campaign filed a further lawsuit to stop the certifying of results, arguing the state subjected in-person voting - which favoured Donald Trump - to greater scrutiny than postal votes.

The Pennsylvania Attorney General said this new lawsuit was "meritless", and experts say it is unlikely to succeed.

The president's campaign has said it will request a recount in Wisconsin "based on abnormalities seen" on election day, although this wouldn't require a lawsuit.

It's unclear when this recount would take place, since typically these don't happen until after officials finish reviewing the votes.

The state's deadline for this part of the process is 17 November.

Columbia University Law School professor Richard Briffault says there was a recount in Wisconsin in 2016 as well, and it "changed about a hundred votes".

Mr Trump won the state in 2016 by his slimmest margin - just over 10,700 votes - and Mr Biden has been projected as the winner here in 2020.

On 4 November, the Trump campaign filed a lawsuit to stop the count over claims of a lack of access to observe the process.

A judge dismissed the lawsuit, saying there was insufficient evidence that oversight procedures weren't being followed.

Another lawsuit was filed on 9 November, seeking to block the certification of results in Wayne County, citing further complaints from poll watchers.

The Nevada Republican Party tweeted saying: "Thousands of individuals have been identified who appear to have violated the law by casting ballots after they moved from Nevada."

A lawsuit filed on 5 November, alleged that "lax procedures for authenticating mail-in ballots over 3,000 instances of ineligible individuals casting ballots."

The president's legal team produced a list of people who it claimed had moved out of state but voted.

But - as pointed out by Politifact - the list alone does not prove a violation of law.

People who leave the state within 30 days before an election can still vote in Nevada. Students and military personnel from Nevada - who are living elsewhere - can also vote.

The case is focused on voters in Clark County, but the county's registrar has said: "We are not aware of any improper ballots that are being processed."

In a separate case filed on 5 November, Republicans tried to stop the use of a signature verification machine at the count - but their attempt was blocked by a federal judge.

A lawsuit was filed in Georgia's Chatham County to pause the count on 4 November, alleging problems with ballot processing.

Georgia Republican chairman David Shafer tweeted that party observers saw a woman "mix over 50 ballots into the stack of uncounted absentee ballots".

On 5 November, a judge dismissed this lawsuit, saying there was "no evidence" of improper ballot mixing.

The Trump campaign filed a lawsuit in Arizona on 7 November, claiming some legal votes were rejected.

The case cites declarations by some poll watchers and two voters who claim they had problems with voting machines.

The lawsuit is under review, but Arizona's Secretary of State said it was "grasping at straws".

On 4 November, Mr Trump claimed voting fraud - without providing evidence - and said: "We'll be going to the US Supreme Court".

If the election result is challenged, it would usually first require legal teams to challenge it in the state courts - although Mr Barr has also approved "preliminary inquiries" by federal prosecutors.

State judges would then need to uphold the challenge and order a recount.

The Supreme Court could then be asked be asked to weigh in.

Prof Briffault says: "There's no standard process for bringing election disputes to the Supreme Court. It's very unusual and it would have to involve a very significant issue."

To date, the 2000 election is the only one to be decided by the US Supreme Court.

In 2000, Democrat Al Gore lost Florida - and the presidential election - by 537 votes out of a total of almost six million cast in the state.

This was followed by a highly controversial recount process that lasted over a month - until the Supreme Court ruled to stop recounting and in favour of Republican George W Bush who became president.