"Due to an outage with one of our systems, tweets on account profiles were visible to some, but not others," the social media site posted on its @TwitterSupport account. As of Sunday morning the message was again visible to Trump's 68 million followers. The tweet identifies a person it says is the whistleblower: the person who first alerted members of Congress to the President's conduct in his July 25 phone call with Ukrainian President Volodymyr Zelensky. For months, Trump has threatened to disclose the identity of the whistleblower, complaining that he should be able to face his accuser. In the past few days, he has inched closer to doing so. On Thursday night, the President retweeted a link to a Washington Examiner story that used the name. The alleged whistleblower has also been named in other conservative media, including Breitbart News. He was named by a contributor on Fox News, and Donald Trump jnr has tweeted the name.

Loading Replay Replay video Play video Play video The whistleblower's identity has been kept secret because of whistleblower protection laws, which exist to shield those who come forward with allegations of wrongdoing by the government. Whistleblower advocates say anonymity is important because it protects those who speak up from retaliation and encourages others to come forward. Trump and his allies claim the law does not forbid disclosing the identity of the whistleblower. Federal laws offer only limited protection for those in the intelligence community who report wrongdoing; those in the intelligence community have fewer protections than their counterparts in other agencies. The 1998 Intelligence Community Whistleblower Protection Act does not detail any protections for whistleblowers from retaliation — instead merely describing the process to make a complaint. Loading

Whistleblower attorney Bradley Moss said in September that the law did not apply to members of Congress who might disclose the whistleblower's name. "This is all very, very fragile, and a lot of the protections that we understand to exist are based more on courtesy and custom than anything written down in law," Moss said. Moss is the law partner of Mark Zaid, one of the whistleblower's attorneys, though he has had no involvement in that case. The whistleblower, who works for the Central Intelligence Agency, filed an official complaint that, among other concerns, pointed to a July 25 phone conversation in which Trump asked Zelensky to investigate former vice-president Joe Biden, a Democratic presidential candidate. After several months of investigation, the House voted on December 18 to impeach Trump on charges of abuse of power and obstruction of Congress. The Senate will hold a trial, where the Republican majority is expected to acquit, in early 2020, once House Speaker Nancy Pelosi transfers the articles of impeachment. Loading

Congressional Republicans have demanded the whistleblower testify as part of the impeachment probe. Democrats have countered that the whistleblower's testimony is unnecessary because other witnesses have corroborated and expanded on the original complaint, which was based on secondhand information. In early November, the whistleblower's attorney sent White House counsel Pat Cipollone a cease-and-desist letter, demanding the President stop denigrating the whistleblower. "I am writing out of deep concern that your client, the President of the United States, is engaging in rhetoric and activity that places my client, the Intelligence Community Whistleblower, and their family in physical danger," wrote attorney Andrew Bakaj. "I am writing to respectfully request that you counsel your client on the legal and ethical peril in which he is placing himself should anyone be physically harmed as a result of his, or his surrogates', behaviour." The whistleblower, who is reportedly still in his job, is driven to and from work by armed security officers when threats are elevated. Threats against him seem to spike whenever Trump tweets about him, previous reports indicate. The Twitter feed for @Surfermom77, who identifies herself as "Sophia" on the social media site, is a daily stream of pro-Trump and anti-Democrat memes and propaganda. In 2016, the account shared the false conspiracy theory that President Barack Obama was Muslim.