WASHINGTON — Hillary Clinton's service as America's third female secretary of State produced few dramatic diplomatic initiatives but was generally highly regarded by foreign policy experts when she stepped down nearly four years ago.

Now the controversy over Clinton's use of a private email server while at the State Department, plus a partisan clash over her response to the 2012 Benghazi attack and the relentless wear-and-tear of global crises, have overshadowed her achievements and could undermine a pillar of her presidential campaign.

After losing her first White House bid in 2008, Clinton became the top U.S. diplomat during President Barack Obama's first term.

By most accounts, Clinton had Obama's ear on critical issues and helped bring professionalism back to a diplomatic corps that was often demoralized under President George W. Bush.

“The first Obama term was much more successful in terms of foreign policy than the second,” said Walter Russell Mead, a foreign policy scholar who edits The American Interest, a publication of political commentary. “But because things have not gone as hoped, while the world got in worse shape, it is harder to talk about (Clinton's) legacy.”

Although Clinton's supporters insist her work helped pave the way, the intense negotiations that led to a historic nuclear arms-control deal with Iran last year, which arguably will be Obama's major foreign policy legacy, began after she left office.

Moreover, some of Clinton's gains overseas, such as restoring diplomatic relations with the shaky democracy in Myanmar after decades of isolation, have faded. The government is still accused of regular human rights abuses.

Obama has called Clinton the most qualified candidate ever to run for the White House. Among the highlights of her tenure, Obama has said, were her counsel and calm in the Situation Room before Obama made the decision to launch the raid in Pakistan that killed Osama bin Laden in May 2011. Clinton's icy focus on detail — a trait she sometimes self-mocks on the campaign trail — was a plus during national security crises.

Experts say Clinton oversaw the negotiations with Russia that led to the New START Treaty to reduce strategic offensive nuclear weapons. She also is credited with putting climate change and women's rights high on the new administration's agenda.

Clinton championed Obama's 2011 call for a strategic and economic “pivot” to Asia and the Pacific Rim, and she supported the Trans-Pacific Partnership, an ambitious 12-nation trade deal then being negotiated. She also advocated resetting troubled relations with Russia.Last October, as a presidential candidate, Clinton withdrew her support for the TPP, saying the final draft did not meet her standards for creating new jobs and “raising wages for Americans.”

Michael O'Hanlon, a national security expert at the Brookings Institution who has advised Clinton, judged her State Department record “more solid than spectacular” when she left office in 2013.

He stands by that assessment but says some of her efforts have borne fruit that was not discernible then, such as the pivot to Asia and attention given to climate change.

Other issues continue to haunt her campaign. Donald Trump, the GOP presidential nominee, has hammered Clinton for her handling of the 2012 attack on a U.S. diplomatic mission and nearby CIA post in Benghazi, Libya, that left a U.S. ambassador and three other Americans dead.

Foreign policy experts are more critical of the administration's failure to help stabilize Libya after a U.S.-led NATO air war helped militants oust strongman Moammar Gadhafi in 2011. The ensuing chaos led to Benghazi and the turmoil that sill engulfs the North African nation.

More damaging is the still-unfolding scandal over Clinton's use of a private email server while she was in office. The FBI closed its investigation without recommending criminal charges, but Clinton can look forward to the release this fall of further emails that critics say show she lied, a charge she denies.

Unable to shed those controversies, the Democratic nominee has focused more on the economy and other domestic issues on the campaign trail.

Clinton has described her foreign policy philosophy as both inclusive and outward-looking due to the optimistic outlook she absorbed with her Methodist upbringing.

“I worked to reorient American foreign policy around what I call ‘smart power,'?” Clinton wrote in her 2014 memoir, “Hard Choices.”

“To succeed in the 21st century,” she wrote, “we need to integrate the traditional tools of foreign policy — diplomacy, development assistance, and military force — while also tapping the energy and ideas of the private sector and empowering citizens, especially the activists, organizers, and problem-solvers we call civil society.”

tracy.wilkinson@latimes.com