President Donald Trump's pick for Secretary of Homeland Security - was confirmed by the Senate in a 62-37 vote Tuesday, further consolidating chief of staff John Kelly's power within the administration.
Kelly left the Department of Homeland Security for the White House in late July during a shakeup that included the resignation of the former chief of staff, Reince Priebus.
Duke was confirmed as deputy DHS secretary in April, but she does not have a close relationship to Nielsen.
Nielsen said at her confirmation hearing last month that climate change is a "crucial issue", noting the Trump administration is revising its climate models to better respond to rising sea level, but said the human impact on climate change is not fully understood.
With more than a third of the Senate voting against her, Nielsen's margin of approval was the narrowest ever for the confirmation of a DHS secretary.
"Ms. Nielsen will be charged with leading the department at a critical time", he said. With her understanding of the challenges facing our nation and her experience in prevention and preparedness, I believe that she will excel as the next Secretary of Homeland Security.
Ten Democrats joined in the vote to confirm Nielsen on December 5, with no Republicans voting against. -Mexican border, saying that she does not support building a wall along the entire length of the border.
When asked for her views on the utility of a border wall with Mexico, she echoed comments made previously by Kelly that the United States did not need a 2,000-mile physical barrier "from sea to shining sea".
In her new position as DHS secretary, Nielsen will oversee about 240,000 employees at Customs and Border Protection, the Transportation Security Administration, the Coast Guard, the Federal Emergency Management Agency, and other agencies.
That statement failed to allay the concerns of Harris - who still voted against Nielsen, who said in a statement that she "equivocated" on Dreamers - and earned her the scorn of the Bannon wing, which has characterized her as a threat to Trump's "populist-nationalist agenda" and an ally of the "Never Trump" movement. Kamala Harris, D-Calif, who voted against Nielsen's nomination, criticized her stances on immigration and the environment, as well as her experience.
Senate Majority Mitch McConnell, R-Ky., called Nielsen a qualified candidate with the talent and experience to succeed.