WASHINGTON (REUTERS, WASHINGTON POST) - United States President Donald Trump's former lawyer Michael Cohen testified on Tuesday (Aug 21) that "at the direction of" the President, he arranged six-figure hush payments ahead of the 2016 presidential election to adult-film actress Stormy Daniels and former Playboy model Karen McDougal.

Both women have said they had affairs with Mr Trump, which he has denied.

Cohen gave his testimony in a New York courtroom as part of a deal with prosecutors in which he pleaded guilty to campaign finance violations, tax evasion and bank fraud.

Mr Trump said on Twitter on Wednesday that the campaign finance violations to which Cohen pleaded guilty were "not a crime", even though prosecutors and Cohen agreed that they were. Mr Trump made the claim without offering any evidence.

His lawyer, Mr Rudy Giuliani, has said the payments were personal in nature and unrelated to the campaign.

The following explains the protections from criminal prosecution that are afforded a US president and how impeachment could be used to remove Mr Trump from office.

1. CAN THE PRESIDENT BE CHARGED WITH A CRIME WHILE IN OFFICE?

The US Constitution does not address this. A number of legal experts have said that a president cannot be indicted while in office, and that if a president committed a crime, the appropriate recourse would be impeachment.

The US Constitution specifies that the president can be impeached for treason, bribery or other "high crimes and misdemeanours".

The US Supreme Court has not ruled on whether a sitting president can be charged with a crime, but in a 2000 memorandum, the Department of Justice concluded that criminal proceedings would impermissibly interfere with the president's ability to carry out his job.

2. HOW DOES THE IMPEACHMENT PROCESS WORK?

The impeachment process starts in the House of Representatives. Individual members can introduce impeachment resolutions like ordinary Bills, or the House can initiate proceedings by passing a resolution authorising an inquiry.

Impeachment requires a simple majority to pass the House, but the removal of the president from office further requires a two-thirds majority in the Senate.

Two American presidents have been impeached: Mr Andrew Johnson in 1868 and Mr Bill Clinton in 1998. In both cases, a majority of the Senate did not approve removal and they remained in office.

If a president is impeached and removed, the vice-president takes over until the next scheduled presidential election.

3. IS A VIOLATION OF CAMPAIGN FINANCE LAW AN IMPEACHABLE OFFENCE?

Legal experts disagree over whether Mr Trump could be impeached based on the allegation that he directed Cohen to make an unlawful campaign contribution.

Congress has latitude to determine "high crimes and misdemeanours." While it has looked to US criminal code for guidance, it is not bound by it, legal experts said.

Mr Andrew Wright, a former associate counsel to former president Barack Obama, said the Cohen guilty plea was sufficient grounds to begin an impeachment investigation.

He said the Constitution suggests that the country's founders were concerned about potential abuses of power, which would include an effort to mislead the public in the run-up to an election.

Other experts have said that Mr Trump could argue that the payments to the women were not a crime because they were made to protect Mr Trump's reputation, not for the purpose of influencing the election.

Even if the payments were intended to influence the election, some legal scholars have argued that campaign finance violations are typically enforced through civil penalties and do not amount to a high crime or misdemeanour. Therefore, impeachment would not be warranted.

4. HOW IS TRUMP'S COMPANY IMPLICATED IN ALL THIS?

It's not just the President who got pulled into Cohen's convictions. Legal filings from the case revealed that executives at Trump Organisation okayed US$420,000 (S$575,000) in reimbursements to Cohen to pay off these women, then tried to hide the true nature of those payments by describing them as legal fees and retainers.

Prosecutors say Cohen even got a US$60,000 bonus for his work trying to keep these women quiet during the election.

That could be legally problematic if a court viewed those reimbursements as another unreported in-kind contribution to Mr Trump's campaign.

5. WHAT ELSE DOES COHEN KNOW ABOUT TRUMP?

Cohen's plea deal didn't specifically say he would help out with investigations into the President, but it's pretty clear he wants to.

Cohen's lawyer dangled this tantalising nugget: Cohen has information that Special Counsel Robert Mueller might be interested in.

Cohen has said Mr Trump knew about that Trump Tower meeting before it happened, the one that investigators think may have involved collusion with Russians.

And Cohen's lawyer, Mr Lanny Davis, said his client knows details of "computer crime of hacking" and "whether Mr Trump knew ahead of time about that crime and even cheered it on".

This might all be bluster. The Washington Post reports that Mr Mueller has determined Cohen isn't necessary to the special counsel's work.

But another possibility is that Cohen knows something that Mr Mueller doesn't know he knows.