Yates is expected to address the concerns that she reportedly raised in January about the veracity of claims made by then–national security adviser Michael Flynn over his conversations with the Russian ambassador to the U.S.
Today, Trump suggested in a tweet that Yates had leaked classified information to the press.
"Ask Sally Yates, under oath, if she knows how classified information got into the newspapers soon after she explained it to W.H. Counsel," he wrote, originally misspelling "counsel" and later correcting it.
At today’s White House press briefing, press secretary Sean Spicer refused to elaborate on the president’s tweet.
"I think the tweet speaks for itself. Sometimes you don't have to read too much into it," Spicer said.
Trump posted another tweet on the topic — but not about Yates directly — nearly 20 minutes earlier. In that tweet, he pointed the finger at the Obama administration for giving Flynn "the highest security clearance."