The Senate had received a coronavirus briefing the day her stock sales began. Ms. Loeffler tweeted about the briefing that day. “Appreciate today’s briefing from the President’s top health officials on the novel coronavirus outbreak,” she wrote. “These men and women are working around the clock to keep our country safe and healthy.”

Other senators have also sold holdings in recent weeks and before the major economic downturn, including Senators Dianne Feinstein, Democrat of California, and James M. Inhofe, Republican of Oklahoma. Those transactions have drawn far less scrutiny.

Ms. Feinstein’s office said her assets were in a blind trust and she was not involved in her husband’s financial decisions. Mr. Inhofe said in a statement that he did not attend the Jan. 24 briefing and that his transactions were part of a sell off that his financial adviser had begun in late 2018, when he became chairman of the Senate Armed Services Committee.

What Burr and Loeffler are saying

Both Mr. Burr and Ms. Loeffler have claimed no wrongdoing.

“This is a ridiculous and baseless attack,” Ms. Loeffler wrote on Twitter early Friday morning. “I do not make investment decisions for my portfolio. Investment decisions are made by multiple third-party advisors without my or my husband’s knowledge or involvement.”

She linked to her financial disclosure report and said, “I was informed of these purchases and sales on February 16, 2020 — three weeks after they were made.”