WASHINGTON — When it came time to select a new chief of staff, President Barack Obama didn’t look very far.

The president announced Friday that he tapped Denis McDonough, one of his most loyal and trusted advisers, for the key job as he launches his second term.

McDonough, 43, has been serving as deputy national security adviser, helping to orchestrate the U.S. military drawdown in Iraq and Afghanistan and the response to the fatal attack on a U.S. diplomatic facility in Benghazi, Libya.

But more than the president’s previous chiefs of staff – Rahm Emanuel, William Daley and Jack Lew – McDonough is an Obama loyalist who has been with him since he was a senator.

Martha Joynt Kumar, a Towson University political science professor who studies the presidency, said the most effective chiefs of staff have a variety of traits, including those who have experience on Capitol Hill and can balance politics and policy.

But for Obama, a president who likes to surround himself with a close-knit circle, being a confidant is helpful.

“He likes to have his team around him,” Kumar said.

In his remarks Friday in the East Room, Obama called McDonough a “great friend” who he has been counting on for nearly a decade.

“Denis, you’re not just one of my closest friends, but you’re also one of my closest advisers, and like everybody here, I cannot imagine the White House without you,” he said.

In 2006, McDonough joined Obama’s Senate staff and later worked on his campaign and transition. When he got to the White House, Obama named McDonough his chief foreign policy communications strategist, and later to the No. 2 job at the National Security Council.

The chief of staff job may not be known by many outside Washington, but it’s one of the most critical in every White House.

It serves as gatekeeper to the president and helps gets his initiatives implemented. Obama plans an aggressive second-term agenda that includes curbing gun violence, overhauling immigration laws and combating global warming.

For years, presidents did not have chiefs of staff. Dwight D. Eisenhower hired the first after determining that the White House had become too large and unwieldy to manage by himself, said James Pfiffner, a George Mason University professor who has researched chiefs of staff.

Presidents Jimmy Carter and Gerald Ford tried to manage without one, but they found that they could not, he said.

“It’s an inside and administrative job, but it’s crucial,” Pfiffner said. “In Washington, it’s one of the powerful positions.”

Obama has seen more turnover in the position than other recent presidents. George W. Bush had just two and Bill Clinton had four, both in eight years.

Emanuel, a former member of Congress, and Lew, a budget expert, had relationships on Capitol Hill, while Daley, a businessman who became commerce secretary, had strong ties to the business community. Obama also tapped aide Pete Rouse to serve for several months in a temporary capacity.

McDonough will replace Jack Lew, who Obama nominated as treasury secretary. He has not been confirmed by the Senate yet.

Since restructuring his staff after several key vacancies at the start of his second term, Obama has been criticized for a less than diverse selection of mostly white men. McDonough’s appointment could continue that criticism, though on Thursday Obama nominated a woman, former federal prosecutor Mary Jo White, to be chairwoman of the Securities and Exchange Commission.

At a recent news conference, Obama said he should be judged on his appointments after he finishes them.

“I would just suggest that everybody kind of wait until they’ve seen all my appointments – who’s in the White House staff and who’s in my Cabinet – before they rush to judgment,” he told reporters.