President Donald Trump has denied any money from his campaign was used to buy an adult film actor’s silence over an affair he says never happened.

He admitted in a tweet lawyer Michael Cohen had paid off Stormy Daniels during the campaign and was reimbursed.

Using campaign funds could have been a violation of federal law. Earlier, his legal aide Rudy Giuliani had said the money was Mr Trump’s personal cash.

Ms Daniels says she had an affair with Mr Trump in 2006.

• Should Trump be worried about Stormy Daniels?
• The president and the porn star: Why this matters
• What are non-disclosure agreements?

What has Mr Trump said?

The president fired off three tweets on Thursday morning.

In them, he admitted that Mr Cohen had “received a monthly retainer, not from the campaign and having nothing to do with the campaign, from which he entered into, through reimbursement, a private contract between two parties, known as a non-disclosure agreement, or NDA”.

Mr Trump’s argument appears to be that the NDA was a typical action taken out by celebrities and therefore not an election-related matter.

This could be crucial in determining whether the $130,000 (£95,650) paid to Ms Daniels was legal.

What are the issues over campaign finance?

US federal law restricts how much individuals and organisations can contribute to campaign financing and there are also strict regulations on the disclosure of the financing.

The key question may be whether the money was used to prevent Mr Trump’s reputation being harmed during the campaign, and therefore be deemed as related to the election.

Legal expert Lawrence Noble told the Washington Post: “If the purpose of this was to stop [Daniels] from hurting the campaign, then what you have is Cohen made a loan to the campaign.”

The $130,000 would exceed the amount an individual can donate to a presidential campaign.

Any repayment by the Trump campaign would violate the law.

But presidential candidates are allowed to contribute an unlimited amount to their own campaign. Mr Trump may be arguing that the personal nature of the repayment makes it legal.

If the $130,000 were deemed to have been a loan to Mr Cohen, the president would only have had to disclose the repayment to the Federal Election Commission if it were an election-related expense.

There is no mention of any debt to Mr Cohen on Mr Trump’s personal financial disclosure form from June 2017.

Has what Mr Trump said squared with Mr Giuliani?

The former New York City mayor recently joined Mr Trump’s legal team and had earlier been interviewed by Sean Hannity on Fox News.

The campaign finance issue appeared to be one his main motives for appearing on the programme.

Mr Giuliani said: “That money was not campaign money… No campaign finance violation.

“They funnelled it through a law firm and the president repaid it.”

He added that the president “didn’t know about the specifics of it, as far as I know, but he did know about the general arrangement that Michael would take care of things like this”.

Mr Giuliani later spoke to the New York Times, saying: “Some time after the campaign is over, they set up a reimbursement, $35,000 a month, out of his personal family account.” The sum paid was $460,000-$470,000, including expenses, he said.

He also said Mr Trump was aware of what he was going to say on Fox News and that he had spoken to the president before and after the interview.

Mr Trump’s tweet also speaks of a monthly retainer, although it is unclear about the timing of its payment to Mr Cohen.

What have the parties previously said?

When asked by reporters a month ago if he knew about the payment to Ms Daniels, Mr Trump said: “No.”

When asked why the payment was given to Ms Daniels, he added: “You’ll have to ask Michael Cohen.”

Mr Giuliani told the Times he did not know whether Mr Trump was aware of the payment to Ms Daniels at the time but his understanding was that the president had only learned about it recently. It is unclear how this fits with his statement that repayments were made over several months.

Speaking on Fox TV last week, Mr Trump suggested some knowledge of the matter in admitting Mr Cohen had represented him during the “crazy Stormy Daniels deal”, but did not go into specifics.

Mr Cohen, for his part, told the New York Times in February: “Neither the Trump Organization nor the Trump campaign was a party to the transaction with Ms Clifford, and neither reimbursed me for the payment, either directly or indirectly.”

How this relates to any personal repayments by Mr Trump is unclear.

What has been the reaction?

Ms Daniels’ lawyer, Michael Avenatti, had said that Americans “should be outraged” at Mr Giuliani’s comments.

“We predicted months ago that it would be proven that the American people had been lied to as to the $130k payment and what Mr Trump knew,” he wrote on Twitter.

He told Associated Press: “Mr Trump evidently has participated in a felony and there must be serious consequences for his conduct and his lies and deception to the American people.”

The BBC’s Anthony Zurcher says Mr Trump has proven bulletproof when it comes to most political scandals and this one may prove no different, although the Stormy saga has proven to have staying power.

Our correspondent says there will still be questions over whether the payment violated campaign finance law.

How did the payment come about and what has happened since?

The payment relates to allegations by Ms Daniels that she had sex with Mr Trump in 2006, allegations he denies.

After initially denying the payment, Mr Cohen eventually admitted he had paid the sum privately to Ms Daniels, real name Stephanie Clifford, in October 2016 out of his own funds in exchange for her silence in a non-disclosure agreement.

He says Mr Trump was not a party to the transaction.

Mr Cohen is now facing a criminal investigation. FBI agents searched his home and office in New York recently in relation to the nondisclosure agreement.

In March this year, Ms Daniels filed a lawsuit against the president, alleging that the agreement was invalid because Mr Trump did not sign it.

She later lost a court motion for Mr Trump to give sworn testimony about her claim that they had a relationship.

While Mr Trump has denied her claims, his lawyers are seeking $20m in damages from Ms Daniels, arguing she broke the non-disclosure deal.

In his tweet on Thursday, Mr Trump said the NDA was to “stop the false and extortionist accusations by her about an affair despite already having signed a detailed letter admitting that there was no affair”.

Ms Daniels is also suing the president over a “defamatory” tweet he posted after she said she was threatened by a man in a Las Vegas car park to drop her allegations of the affair.

Mr Trump had said her claims were “a total con job”.