By SCOTT SHANE New York Times

How did U.S. intelligence officials come to brief President Obama, President-elect Donald Trump and lawmakers about supposed Russian plans to try to blackmail Trump? There are far more questions than answers. But here is a look at the story so far.

What we know

— Last year, a Washington political research firm, paid by Trump's Republican rivals, hired a retired British intelligence officer to investigate the candidate's ties to Russia.

— After it became clear that Trump would be the Republican nominee, Democratic clients began to pay the firm for this same "opposition research," standard practice in politics.

— The former British spy, who had long experience in Russia and a network of connections there, compiled dozens of reports detailing what he heard from his contacts. The memos he wrote, mostly one to three pages long, are dated from June to December.

— The memos contain unsubstantiated claims that Russian officials tried to obtain influence over Trump by preparing to blackmail him with sex tapes and bribe him with business deals. They also claim that the Trump campaign met with Russian operatives to discuss the Russians' hacking and their leaking of e-mails and documents from the Democratic National Committee and from Hillary Clinton's campaign chairman, John D. Podesta.

— The Washington firm and the former British spy, not identified here because of a confidential source agreement with the New York Times, gave the memos first to their clients but later to the FBI and multiple journalists at The Times and elsewhere. The memos, totaling about 35 pages, also reached a number of members of Congress.

— Last week, when the FBI, CIA and National Security Agency gave a classified report on the Russian hacking and leaking and efforts to influence the presidential election to Obama, Trump and congressional leaders, they attached a two-page summary of the unverified allegations in the memos.

What we don't know

— Whether any of the claims in the memos are true. U.S. intelligence agencies have not confirmed them, and Trump has said they are a complete fabrication. In addition, one specific allegation — that Trump's lawyer, Michael Cohen, met with a Russian official in Prague in August or September — has been denied by both Cohen, who says he has never been to Prague, and the Russian, Oleg Solodukhin.

— Who concocted the information in the memos, if it is entirely false or partly so, and with what purpose. Did the British intelligence officer accurately report what he heard? Who gave him the information that, if false, amounts to a very sophisticated fabrication?

— What exactly prompted U.S. intelligence officials to pass on a summary of the unvetted claims to Obama, Trump and Congress. Officials have said they felt the president-elect should be aware of the memos, which had circulated widely in Washington. But why put the summary in a report going to multiple people in Congress and the executive branch, virtually assuring it would be leaked?

— What will happen now. The FBI has been investigating the claims in the memos, and Democrats are demanding a thorough inquiry into the reports that Trump representatives met with Russian officials during the campaign. But as of Jan. 20, Trump will be in charge of the bureau and the other intelligence agencies, and he may not approve such an investigation.

— Why did the Times and other outlets report extensively on the hacking of Democratic Party, but not this?

The Times did report before the election that the FBI was investigating claims about Trump's ties to Russia — an article that resulted from an extensive reporting effort. The Democratic National Committee and Podesta e-mails were public, their authenticity was not in doubt and they contained newsworthy information.

— Why did the FBI director write two letters about Clinton's e-mails before the election, but not this?

That is a question Comey may eventually have to answer. His two public statements about the bureau's investigation of the Clinton e-mails were highly unusual and a break with long FBI tradition.

— Why did the news media not raise this during the campaign?

Many reporters from multiple news organizations tried to verify the claims in the memos but were unsuccessful. That does not mean that none of the claims are true, but most news organizations choose not to publish damaging allegations against a public figure unless they believe them to be true.

— Why is this now being reported?

CNN broke the news that a summary of the memos had been attached to the classified report by the FBI, CIA and National Security Agency on the Russian hacking and leaking during the presidential election and that it was given to Obama, Trump and congressional leaders last week. That level of official attention prompted news media organizations to decide to inform the public about the memos.