WILMINGTON, Del. (AP) — Declaring "America is back," President-elect Joe Biden introduced selections for his national security team Tuesday, his first substantive offering of how he’ll shift from Trump-era “America First” policies by relying on foreign policy and national security experts from the Democratic establishment to be some of his most important advisers.

Biden’s Washington veterans all have ties to former President Barack Obama’s administration as the president-elect has sought to deliver a clear message about his desire to reestablish a more predictable engagement from the United States on the global stage.

“It’s a team that reflects the fact that America is back, ready to lead the world, not retreat from it,” said Biden, at an introductory event at which his selections stood on stage, at least six feet apart and masked.

The president-elect’s team includes Antony Blinken, a veteran foreign policy hand well-regarded on Capitol Hill whose ties to Biden go back some 20 years, for secretary of state; lawyer Alejandro Mayorkas to be homeland security secretary; veteran diplomat Linda Thomas-Greenfield to be U.S. ambassador to the United Nations; and Obama White House alumnus Jake Sullivan as national security adviser.

Avril Haines, a former deputy director of the CIA, was picked to serve as director of national intelligence, the first woman to hold that post, and former Secretary of State John Kerry will make a curtain call as a special envoy on climate change. Kerry and Sullivan’s position will not require Senate confirmation.

With the Senate’s balance of power hinging on two runoff races in Georgia that will be decided in January, some Senate Republicans have already expressed antipathy to Biden’s picks as little more than Obama world retreads.

Sen. Tom Cotton, an Arkansas Republican and potential 2024 GOP presidential hopeful, derisively accused Biden of surround himself with “panda huggers” who will go soft on China. Sen. Marco Rubio, who sits on the Senate Foreign Relations Committee that will consider Blinken’s nomination, broadly wrote off the early selections as uninspiring.

“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.

But Biden’s transition team hailed the president-elect’s selection as a group of “crisis-tested leaders” who will be ready to hit the ground running in the new administration.

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 Obama to lead the Federal Reserve, the first woman in that position, and served from 2014 to 2018.

Biden said his choices “reflect the idea that we cannot meet these challenges with old thinking and unchanged habits.” He said he tasked them with reasserting global and moral leadership.

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 world capitals. And with a roster that includes 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.

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.

Meanwhile, there were signs on Tuesday that the stalled formal transition of power is now underway.

The Pentagon said Tuesday that Kash Patel, the chief of staff to the acting secretary of defense, 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.

The move came a day after the head of the General Services Administration wrote the necessary letter of “ascertainment” acknowledging Biden as the apparent winner of election, triggering the transition process.

The ascertainment gives the incoming president and his team access to officials at federal agencies and directs the Justice Department to work on security clearances for transition team members and Biden political appointees.

It even gives his team access to official government website domains and releases $6.3 million in congressionally appropriated funds to Biden’s transition team and 175,000 square feet (16,200 square meters) of federal office space, including secure areas where Biden and his team can receive sensitive intelligence briefings.

Trump, who continues to press a legal challenge to overturn the election results, again on Tuesday refused to concede his election loss.

Trump tweeted that “the GSA does not determine who the next President of the United States will be.”