Washington (AFP) - Donald Trump said Thursday he has been indicted in the investigation over the improper handling of classified documents, in a case that would make him the first US president past or present to face federal criminal charges.

But the matter is far from the only legal peril dogging the ex-leader as he seeks a return to the White House in 2024.

The rebellious Republican billionaire was already charged in a New York state case in March over hush money paid to a porn star who says they had an affair -- and he faces additional federal and state investigations.

Trump made the announcement about the documents probe indictment Thursday evening via his Truth Social platform, but denied any wrongdoing. 

"I AM AN INNOCENT MAN!" he wrote, adding, "This is indeed a DARK DAY for the United States of America."

Here are the key investigations underway against the 76-year-old one-term president:

Secret documents at home

Special counsel Jack Smith is leading the ongoing investigation into classified documents found at Trump's Florida home -- and over possible obstruction of the probe.

An FBI search of Trump's palatial Mar-a-Lago residence last August turned up classified documents taken when he left office in early 2021.

The raid was triggered by a review of records which Trump finally surrendered to authorities in January 2022.

The Justice Department began investigating after the 15 boxes were found to contain national defense information, including 184 documents marked as confidential, secret or top secret.

It was not yet clear what the exact charges might be.

Trump said on Truth Social that he was "summoned to appear at the Federal Courthouse in Miami on Tuesday, at 3 PM."

Stormy hush money?

A New York grand jury in March indicted Donald Trump over hush money payments made to the pornographic film actress known as Stormy Daniels.

Prior to the 2016 election, intense behind-the-scenes negotiations were held to prevent the leak of an embarrassing revelation that Trump had a relationship with Daniels, whose real name is Stephanie Clifford, in 2006 -- a year after he married his current wife.

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

After US media broke the story, Cohen cooperated with prosecutors and pleaded guilty in 2018 to charges of tax and bank fraud, as well as violating federal campaign financing laws.

Cohen testified that the Trump Organization reimbursed Cohen for his payment to Daniels, which prosecutors said amounted to an undeclared campaign gift in violation of election financing laws.

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

- Incited Capitol attack? -

The independent prosecutor Smith will also decide whether to charge anyone alleged to have "unlawfully interfered with the transfer of power" after the 2020 election or during certification by Congress of the results.

On January 6, 2021, a mob of Trump supporters stormed the US Capitol seeking to stop that certification.

Just before the assault, Trump delivered a fiery speech nearby urging the crowd to "fight like hell."

In explosive hearings separate from the Justice probe, lawmakers argued Trump knew he lost the election yet pressed fake claims of fraud.

They also presented evidence of alleged misconduct by Trump leading up to the insurrection, including accusations he attempted to co-opt government departments into his bid to overturn the election results.

Federal prosecutors have obtained convictions of or guilty pleas from more than 500 people for participating in the uprising, but it remains unclear if Trump will face charges for any plotting or fomenting of the Capitol attack.

Other probes

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

It marked the first time Trump faced legal consequences over a string of sexual assault allegations dating back decades -- and the former leader immediately rejected the verdict as a "disgrace."

Separately, the former president is being investigated for pressuring officials in the southern swing state of Georgia to overturn Biden's 2020 victory -- including a taped phone call in which he asked the 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 and interference.

Earlier this year, the grand jury forewoman, in unusually public remarks, 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.

In New York, meanwhile, the state attorney general Letitia James has filed a civil suit against Trump and three of his children, accusing them of fraud by overvaluing assets to secure loans and then undervaluing 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.