BRANCHBURG, N.J. -- Sally Yates, a top Justice Department official in the Obama administration, is set to testify on Monday about Russia's attempts to interfere in the presidential election.

Yates was fired by the Trump administration in January after refusing to defend the president's travel ban in court.

Ahead of Monday's Senate Judiciary hearing on Russia, President Trump focused on Democrats Sunday morning.

"When will the Fake Media ask about the Dems dealings with Russia & why the DNC wouldn't allow the FBI to check their server or investigate?" he tweeted.

When will the Fake Media ask about the Dems dealings with Russia & why the DNC wouldn't allow the FBI to check their server or investigate? — Donald J. Trump (@realDonaldTrump) May 7, 2017

Yates will testify for the first time about her warnings to the Trump White House regarding former national security adviser, Gen. Michael Flynn.

"She apparently has some information as to who knew what when, that she is willing to share," said Senate Judiciary Committee member Dianne Feinstein.

Deputy Attorney General Sally Yates speaks during a news conference at the Justice Department in Washington June 28, 2016. J. David Ake, AP

"The new national security adviser talking to ambassadors from around the world, there's nothing wrong with that," said Republican committee member, Senator Roy Blunt.

Blunt said Flynn's contacts aren't suspicious, but lying about it is.

"What was particularly wrong was General Flynn not being truthful about the substance of what he said," Blunt added, speaking on NBC's "Meet the Press."

Meanwhile, President Trump's son-in-law and adviser, Jared Kushner, is facing questions about conflicts of interest as reports emerged that his sister, Nicole Meyer, spent the weekend promoting the family business and controversial EB-5 visas in China. The visas grant wealthy foreigners and their families a conditional two-year green card after investing at least $500,000 in U.S. businesses.

In a statement, his personal lawyer told CBS News that Kushner "has no involvement" with his previous companies, "divested his interests," and is not a beneficiary of the family trust.

A Kushner Companies spokesperson also sent CBS News a statement apologizing on behalf of Ms. Meyer if "mention of her brother was in any way interpreted as an attempt to lure investors."