U.S. President Donald Trump on Monday defended hush money payments reported by his former lawyer, responding a day after Democratic lawmakers said Trump could face impeachment and jail time if the transactions are proven to violate campaign finance laws.

Trump said on Twitter that Democrats were wrongly targeting "a simple private transaction."

Court filings last week drew renewed attention to six-figure payments made during the 2016 presidential campaign by Trump's personal lawyer to two women so they would not discuss their alleged affairs with the candidate.

U.S. Rep. Jerrold Nadler, who will lead the judiciary committee when Democrats take control of the House of Representatives next month, said on Sunday that if the payments were found to violate campaign finance laws it would be an impeachable offence.

His Democratic counterpart on the intelligence committee, Rep. Adam Schiff, said Trump could be indicted once he leaves office and could "face the real prospect of jail time."

Payments under scrutiny

Under U.S. law, campaign contributions, defined as things of value given to a campaign to influence an election, must be disclosed. Such payments are also limited to $2,700 US per person.

Earlier this year, Trump acknowledged repaying his former lawyer Michael Cohen for the $130,000 paid to porn star Stephanie Clifford, also known as Stormy Daniels. He previously disputed knowing anything about the payments.

On Monday, the president again denied wrongdoing and sought to shift any blame to Cohen. One post misspelled the word "smoking" twice, drawing criticism and ridicule on Twitter.

“Democrats can’t find a Smocking Gun tying the Trump campaign to Russia after James Comey’s testimony. No Smocking Gun...No Collusion.” <a href="https://twitter.com/FoxNews?ref_src=twsrc%5Etfw">@FoxNews</a> That’s because there was NO COLLUSION. So now the Dems go to a simple private transaction, wrongly call it a campaign contribution,... —@realDonaldTrump ....which it was not (but even if it was, it is only a CIVIL CASE, like Obama’s - but it was done correctly by a lawyer and there would not even be a fine. Lawyer’s liability if he made a mistake, not me). Cohen just trying to get his sentence reduced. WITCH HUNT! —@realDonaldTrump

Trump has denied affairs with Stormy Daniels and the other woman who Cohen said was given hush money, former Playboy model Karen McDougal.

U.S. prosecutors on Friday sought prison time for Cohen, Trump's self-proclaimed "fixer," for the payments they said were made in "co-ordination with and at the direction of" Trump, as well as on charges of evading taxes and lying to Congress.

The case stemmed from a federal investigation into alleged Russian interference in the 2016 presidential election and possible collusion with Trump's campaign. Russia has denied interfering, and Trump has said his campaign did not co-operate with Moscow.

Legal experts are divided over whether a sitting president can be charged with a crime, as well as on whether a violation of campaign finance law would be an impeachable offence.