The tweets came after CBS News reported Nielsen was meeting with President Trump Sunday afternoon.
Nielsen took over for John Kelly, as the head of DHS after he vacated the role to serve as White House chief of staff. Kelly left the White House at the end of 2018.
Prior to her time in Trump’s Cabinet, Nielsen served in the George W. Bush administration in the Transportation Security Administration and on the Homeland Security Council.
The Senate confirmed Nielsen, 62-37, with 10 Democrats and Sen. Angus King (I-Maine) supporting her nomination.
Updated at 6:12 p.m.