Donald Trump's former personal lawyer and ‘fixer’, Michael Cohen, has pleaded guilty to campaign finance violations and alleged the president directed him to pay hush money to two women.
Here are some of the key questions around the development.
Does Cohen's guilty plea mean Mr Trump broke the law?
Cohen said in court that he made one payment ‘in coordination and at the direction of a candidate for federal office’ and the other ‘under direction of the same candidate’.
The amounts and dates all line up with the payments made to porn star Stormy Daniels and former Playboy model Karen McDougal.
Prosecutors did not go as far as Cohen did in open court in pointing the finger at the president, saying Cohen acted ‘in coordination with a candidate or campaign for federal office for purposes of influencing the election’.
Why did they phrase it like that?
Legal experts said there could be multiple reasons for the government lawyers' more cautious statements.
Daniel Petalas, former prosecutor in the Justice Department's public integrity section, said the issue of whether Mr Trump violated the law comes down to whether the then-presidential candidate ‘tried to influence an election, whether he knew and directed it and whether he knew it was improper’.
But Mr Trump's attorney Rudy Giuliani said in a statement: ‘There is no allegation of any wrongdoing against the President in the government's charges against Mr. Cohen.’
Does Cohen's plea relate to the Russia investigation?
The Cohen case was not part of special counsel Robert Mueller's probe into Russian interference in the 2016 election.
It was handled by prosecutors in New York. Still, it could give Mr Mueller a boost.
Laurie Levenson, a former federal prosecutor and professor at Loyola Law School in Los Angeles, argued that Cohen's plea undermines the argument that the investigations swirling around Mr Trump are a ‘witch hunt’, as the president has called Mr Mueller's Russia investigation.
Does Cohen's plea mean Mr Trump could be forced to answer questions?
Mr Trump's lawyers have been negotiating with Mr Mueller about whether the president would be interviewed as part of his Russia investigation.
Now Ms Daniels' attorney Michael Avenatti says he will renew efforts to get Mr Trump to submit to a deposition in a lawsuit the porn star filed to invalidate a nondisclosure agreement she signed ahead of the 2016 election.
Ms Daniels' case is currently on hold, but Mr Avenatti said he will be looking to get the hold lifted.
Is there a precedent?
The US Supreme Court in 1997, ruling in a sexual harassment lawsuit brought by Paula Jones against former president Bill Clinton, held that a sitting president could be made to answer questions as part of a lawsuit.
But that ruling did not directly address whether a president could be summoned to give evidence in a criminal investigation, a question the Supreme Court may have to confront if Mr Mueller tries to compel Mr Trump's to give evidence in his probe.
If there is evidence of wrongdoing, can the president be indicted?
The US Justice Department's Office of Legal Counsel, which provides legal advice and guidance to executive branch agencies, has held that a sitting president cannot be indicted.
Mr Trump's lawyers have said that Mr Mueller plans to adhere to that guidance, though Mr Mueller's office has never independently confirmed that.
There would presumably be no bar against charging a president after he or she leaves the White House.
Could Mr Trump pardon himself?
Mr Trump has already shown he is not afraid to use his pardon power, particularly for those he has viewed as unfair victims of partisanship.
He pardoned a former Arizona sheriff who clashed with a judge on immigration and a Bush administration official convicted of perjury and obstruction of justice in a leak case.
As for whether a president can pardon himself, not surprisingly, courts have never had to answer that question.
Mr Giuliani has himself would be ‘unthinkable and probably lead to immediate impeachment’.
Still, Mr Giuliani argued that Trump ‘probably does’ have the power to pardon himself.