WILMINGTON, Del. (AP) — President-elect Joe Biden is set to introduce his national security team to the nation as he taps Obama administration alumni and other public-service veterans, signaling a shift from the Trump administration’s “America First” policies and a return to U.S. global engagement.

Members of that team are slated to join Biden and Vice President-elect Kamala Harris in person in Wilmington, Delaware, on Tuesday afternoon, where they’ll deliver their first remarks as Biden’s nominees. Among them is former Secretary of State John Kerry, who will take the lead on climate change.

Outside the realm of national security and foreign policy, Biden is expected to choose Janet Yellen as the first woman to become treasury secretary. She was nominated by President Barack Obama to lead the Federal Reserve, the first woman in that position, and served from 2014 to 2018.

Biden's emerging Cabinet marks a return to a more traditional approach to governing, relying on veteran policymakers with deep expertise and strong relationships in Washington and global capitals. And with a roster with multiple women and people of color — some of whom are breaking historic barriers in their posts — Biden is acting on his campaign promise to lead a team that reflects the diversity of America.

The incoming president will nominate longtime adviser Antony Blinken to be secretary of state; lawyer Alejandro Mayorkas to be homeland security secretary; Linda Thomas-Greenfield to be U.S. ambassador to the United Nations; and Jake Sullivan as national security adviser. Avril Haines, a former deputy director of the CIA, will be nominated as director of national intelligence, the first woman to hold that post.

Thomas-Greenfield is Black, and Mayorkas is Cuban American.

Mayorkas might pose the most difficult confirmation challenge from Biden's early round of nominees.

The Senate previously confirmed him in December 2013 by a party-line vote to be the deputy secretary of Homeland Security. The Senate was controlled by Democrats then, and all Senate Republicans voted against Mayorkas’ confirmation mainly because he was then under investigation by the Obama-appointed inspector general in that department. At the time, the Senate historian's office said it was unprecedented for the Senate to vote on a nominee who was under investigation.

The inspector general, John Roth, found in March 2015 that Mayorkas, as director of the U.S. Citizenship and Immigration Services, appeared to give special treatment to certain people as part of the visa program that gives residency preference to immigrants who agree to invest in the U.S. economy.

Sen. Marco Rubio, a Florida Republican, on Tuesday broadly slammed Biden's picks as unworthy.

“Biden’s cabinet picks went to Ivy League schools, have strong resumes, attend all the right conferences & will be polite & orderly caretakers of America’s decline,” Rubio tweeted.

Those being introduced on Tuesday “are experienced, crisis-tested leaders who are ready to hit the ground running on day one,” Biden's transition team said in a statement. “These officials will start working immediately to rebuild our institutions, renew and reimagine American leadership to keep Americans safe at home and abroad, and address the defining challenges of our time — from infectious disease, to terrorism, nuclear proliferation, cyber threats, and climate change.”

In the weeks ahead, Biden could also name Michèle Flournoy as the first woman to lead the Defense Department. Pete Buttigieg, the former Indiana mayor and onetime presidential candidate, has also been mentioned as a contender for a Cabinet agency.

The Pentagon said Tuesday that Kash Patel, chief of staff to the acting defense secretary, is heading the department’s transition work. A transition task force has been assembled, led by Tom Muir, the head of the Pentagon office that provides administrative and management services to all Defense Department facilities in the Washington area.

In making the choices public on Monday, Biden moved forward with plans to fill out his administration even as President Donald Trump refuses to concede defeat in the Nov. 3 election, has pursued baseless legal challenges in several key states and worked to stymie the transition.

Nevertheless Trump said Monday he was directing his team to cooperate on the transition while vowing to keep up the fight. His comment came after the General Services Administration ascertained that Biden was the apparent winner of the election, clearing the way for the start of the transition from Trump’s administration and allowing Biden to coordinate with federal agencies on plans for taking over on Jan. 20.

Beyond Rubio's broadside, Biden's nominations were generally met with silence on Capitol Hill, where the Senate's balance of power hinges on two runoff races that will be decided in January.

The best known of the picks is Kerry, who made climate change one of his priorities while serving as Obama's secretary of state, during which he also negotiated the Iran nuclear deal and the Paris climate accord. Trump withdrew from both agreements, which he said represented a failure of American diplomacy in a direct critique of Kerry, whom he called the worst secretary of state in U.S. history.

Blinken, 58, served as deputy secretary of state and deputy national security adviser during the Obama administration.

He served on the National Security Council during the Clinton administration before becoming staff director for the Senate Foreign Relations Committee when Biden was chairman of the panel. In the early years of the Obama administration, Blinken returned to the council and was Biden’s national security adviser when Biden was vice president, then moved to the State Department to serve as deputy to Kerry.

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Lee reported from Washington. Associated Press writers Michael Balsamo, Robert Burns, and Andrew Taylor in Washington and Bill Barrow in Atlanta contributed to this report.