Washington (AFP) - Former US president Donald Trump is facing four criminal indictments, all filed since March -- with the Republican frontrunner in the 2024 White House race possibly navigating a series of trials as he campaigns.

On Thursday, he was formally arrested on 13 counts in the southern state of Georgia in connection with his alleged efforts to interfere with the results of the 2020 election, which he lost to Democrat Joe Biden.

Trump has already been indicted in federal court in connection with election interference in multiple states, and over his handling of classified documents, making him the first former US president to face federal criminal charges.

The twice-impeached Trump has also been charged in New York with making election-eve hush money payments to a porn star.

Here are the key cases involving the 77-year-old one-term president -- and others that could materialize:

Georgia election meddling

Trump stands accused in Georgia of pressuring state officials to overturn Biden's election victory -- incidents that were also referred to in a federal indictment.

Evidence includes a taped phone call in which he asked Georgia's then-secretary of state to "find" enough votes to reverse the result.

Fulton County's top prosecutor Fani Willis has charged Trump with 13 felony counts including violating Georgia's Racketeer Influenced And Corrupt Organizations (RICO) Act, as well as six conspiracy counts over alleged efforts to commit forgery, impersonate a public official and submit false statements and documents.

Eighteen co-defendants also were indicted, including Trump's former personal lawyer Rudy Giuliani, for pressuring local legislators over the result after the election, and Trump's White House chief of staff, Mark Meadows.

- 2020 election interference -

Special Counsel Jack Smith had already slapped Trump with four federal charges related to efforts to overturn the 2020 election results.

Trump is charged with conspiracy to defraud the United States, as well as conspiracy to obstruct and obstruction of an official proceeding -- the January 6, 2021, meeting of a joint session of Congress held to certify Biden's election victory.

He is also charged with conspiracy to deny Americans the right to vote and to have one's vote counted. 

The indictment mentions six co-conspirators but none are identified -- Trump, currently the frontrunner for the 2024 Republican presidential nomination, is the only named defendant.

Trump supporters stormed the US Capitol on January 6, 2021, as Congress met to certify the presidential election results.

Before what was ultimately a deadly attack, Trump delivered a fiery speech urging the crowd to "fight like hell."

Classified documents

Trump, in another indictment brought by Smith, is accused of endangering national security by holding onto top secret nuclear and defense documents after leaving the White House.

Trump kept the files -- which included records from the Pentagon, CIA and National Security Agency -- unsecured at his Mar-a-Lago home in Florida and thwarted official efforts to retrieve them, according to the indictment.

Trump was initially charged with 31 counts of "willful retention of national defense information," each punishable by up to 10 years in prison. A count was added related to a classified document "concerning military activity in a foreign country." 

He also faces charges of conspiracy to obstruct justice, making false statements and other offenses.

The federal judge in the case has set a trial date of May 20, 2024, at the height of the presidential campaign.

Stormy

A New York grand jury indicted Trump in March over alleged hush money payments made to porn star Stormy Daniels.

Prosecutors say the money was paid prior to the 2016 election to silence Daniels over claims she had a tryst with Trump in 2006 -- a year after he married Melania Trump.

Late in the campaign, Trump's lawyer Michael Cohen arranged a payment of $130,000 to Daniels in exchange for her pledge of confidentiality, prosecutors said.

That case, in which he faces 34 felony counts, is due to go to trial next March, in the middle of the Republican primary election season.

Other probes

Trump was found liable in a civil case for sexually abusing and defaming a former magazine columnist, E. Jean Carroll, in 1996, and ordered to pay her $5 million in damages.

In New York, state attorney general Letitia James has filed a civil suit against Trump and three of his children, accusing them of fraud by over-valuing assets to secure loans and then under-valuing them to minimize taxes.

James is seeking $250 million in penalties as well as banning Trump and his children from serving as executives at companies in the city.

Trump has denied all wrongdoing.