- Prosecutors in New York are investigating alleged hush money payments made on Mr Trump's behalf to Stormy Daniels, a former adult film star who went public with claims the pair had an affair.
- Mr Trump denies they had sexual relations.
Donald Trump is under investigation for everything from his handling of top secret documents to alleged payments made to a former adult film star - and he is facing numerous lawsuits as well.
It can be difficult to keep track of the investigations, so here's four that could have the biggest impact on him both personally and politically.
What's being investigated?
Prosecutors in New York are investigating alleged hush money payments made on Mr Trump's behalf to Stormy Daniels, a former adult film star who went public with claims the pair had an affair.
Mr Trump denies they had sexual relations.
Meanwhile, the business practices of his family company, the Trump Organization, is being examined by prosecutors.
Letitia James, the New York attorney general, is leading a civil investigation (which cannot result in criminal charges) and has spent years looking at whether the company committed various acts of fraud over several decades.
The years-long criminal investigation, meanwhile, is being led by the Manhattan District Attorney Alvin Bragg, and is looking at similar issues.
What has Trump said?
A member of his legal team told the Associated Press that there was no legal basis for the Stormy Daniels case and he did not believe prosecutors had made a decision on charges.
Separately, the former president and his lawyers have insisted the allegations against the Trump Organization are politically motivated.
Mr Trump has repeatedly criticised both Ms James and Mr Bragg.
So how serious is it?
In the Stormy Daniels case, Mr Trump, has been invited to testify to a grand jury. Experts suggest this indicates he could soon face criminal charges, but it is not clear what these could be.
If prosecutors proceed it would be the first criminal case ever brought against a former US president.
The criminal Trump Organization investigation has already yielded convictions. The company was found guilty in December of fraud and falsifying business records and fined $1.6m (£1.31m).
In the civil case, Ms James has filed a lawsuit against Mr Trump and three of his children accusing them of "astounding" fraud and deception.
The lawsuit alleges that the family inflated their net worth by billions, and is seeking $250m (£226m) that was allegedly obtained through fraudulent means. It's also seeking bans on Mr Trump and his children from serving in a leadership role in any New York business.
The case will be decided by a Manhattan judge later this year.
What's being investigated?
The Department of Justice is looking into the removal of government documents from the White House, which were then taken to Mr Trump's Florida estate, Mar-a-Lago, after he left office. Investigators are assessing how these documents were stored and who may have had access to them.
The former president's sprawling beachside property was searched in August and 11,000 documents were seized including around 100 marked as classified. Some of these were labelled top secret.
Unsurprisingly, we know very little about what's in the documents at this stage. But classified material usually contains information that officials feel could damage national security if made public.
What has Trump said?
He's denied wrongdoing and criticised the justice department's investigation, branding it "politically motivated" and a "witch-hunt".
He has offered shifting defences which have mostly hinged on the argument that he declassified the material. No evidence has yet been provided that this is true.
The former president has also argued that some of the documents are protected by "privilege" - a legal concept that would prevent them from being used in future proceedings. An independent lawyer is reviewing the seized material to determine if this is the case and that process continues.
But Mr Trump has not directly addressed the key question of why the documents were at Mar-a-Lago in the first place.
So how serious is it?
This is an active criminal investigation and could result in charges being filed.
Among other statutes, the justice department believes Mr Trump may have violated the Espionage Act by keeping national security information that "could be used to the injury of the United States".
And as well as charges relating to the classified documents themselves, prosecutors are also looking at obstruction of justice as another potential crime.
Mr Trump's team are now locked in a legal battle with the justice department over the investigation.
The department has appointed an independent lawyer, or special counsel, to oversee all of its criminal investigations into Mr Trump. Jack Smith will lead its various inquiries and will ultimately decide whether to bring charges.
What's being investigated?
Mr Trump's alleged role in the attack on the US Capitol on 6 January 2021, when a mob of his supporters stormed the building in an effort to stop the confirmation of President Joe Biden's election victory, is under scrutiny from several federal government bodies.
The most visible has been a congressional committee that spent 18 months looking into Mr Trump's actions. They held a series of televised hearings laying out their case that his election fraud claims led directly to the riot.
Following these hearings, the committee accused Mr Trump of inciting insurrection and other crimes.