WASHINGTON -- President Donald Trump fired Sally Yates as acting attorney general on Jan. 30, after the Obama administration holdover refused to back Trump's controversial travel ban.

On Monday, though, Yates is slated to appear before Congress to tell about what she did four days prior: Alert the White House that Michael Flynn, then Trump's national security adviser, had lied about his contacts with Russia's ambassador.

Flynn's misrepresentations to officials — Vice President Pence included — made him vulnerable to blackmail, Yates said. That led to Flynn's resignation. Now all eyes will be on Yates as she's expected to recount her January revelation.

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When Trump fired Yates, who is from Atlanta, he released a statement saying she "betrayed the Department of Justice by refusing to enforce a legal order designed to protect the citizens of the United States. This order was approved as to form and legality by the Department of Justice Office of Legal Counsel.

“Ms. Yates is an Obama Administration appointee who is weak on borders and very weak on illegal immigration.”

USA TODAY's Kevin Johnson writes "It's perhaps the most-anticipated congressional hearing since FBI Director James Comey publicly acknowledged last month that the bureau was investigating possible collusion between Trump campaign associates and Russian officials."