Former US president Donald Trump is now facing three criminal indictments, all filed since March -- raising the prospect that the Republican frontrunner in the 2024 White House race could end up navigating a series of trials as he campaigns.

On Tuesday, he was indicted on four federal counts in connection to his alleged efforts to interfere with the results of the 2020 election, which he lost to Democrat Joe Biden.

Trump has already been indicted over his handling of top secret classified documents, making him the first former US president to face federal criminal charges.

The twice-impeached Trump, who is seeking to return to the White House in 2024, 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:

- 2020 election interference -

Special Counsel Jack Smith unveiled four new charges against Trump related to efforts to overturn the 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. 

"Each of these conspiracies... targeted a bedrock function of the United States federal government: the nation's process of collecting, counting, and certifying the results of the presidential election," the indictment said.

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 -- an assault that left at least five people dead and 140 police officers injured.

Before the Capitol 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. An additional count was added last week. 

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

Last week, a superseding indictment also added an extra count under the Espionage Act related to Trump allegedly retaining a classified document "concerning military activity in a foreign country." 

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

- Stormy hush money -

A New York grand jury indicted Trump in March over 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.

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.

- Georgia election meddling -

Trump is also being investigated in the southern state of Georgia for pressuring officials there to overturn Biden's 2020 election victory -- incidents that were also referred to in Tuesday's 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.

The top prosecutor in Georgia's Fulton County, Fani Willis, has assembled a special grand jury that could see Trump facing conspiracy charges connected to election fraud.

In unusually public remarks, the grand jury's forewoman in February said the 23-member panel had recommended indictments of multiple people, including "certainly names that you would recognize." 

She did not say whether Trump was among them.

- Other probes -

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

In New York, the 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 New York.

Trump has denied all wrongdoing.

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