Conservatives are pushing back against the appointment of a prominent career State Department official who served as a top aide to former Secretary of State Hillary Clinton and worked closely with her in the immediate aftermath of the Benghazi attacks as ambassador to Colombia.

President Donald Trump is leaning toward nominating Joseph MacManus, a 30-year veteran of the foreign service, to become ambassador to Colombia, several GOP sources tell the Washington Free Beacon.

MacManus is the frontrunner and has the strong support of Tom Shannon, a career foreign service diplomat who serves as undersecretary for political affairs and is considered Secretary of State Rex Tillerson’s right-hand man.

Before MacManus emerged as the top candidate, the current ambassador to Peru, Brian Nichols, who has extensive experience in Latin American affairs, was slated for the post. His advocates believe he has far more expertise in the region than MacManus while not suffering from the Clinton baggage.

The outgoing ambassador, Kevin Whitaker, spent several years in Latin America, including serving in Honduras, Nicaragua, and Venezuela, where he was deputy chief of mission from 2005 to 2007. MacManus's experience in the region is limited to a few years in public diplomacy positions in Mexico and El Salvador for the U.S. Information Agency between 1986 and 2003, according to his bio.

Colombia is Washington's staunchest ally in Latin America, and the top U.S. diplomatic post in Bogota carries new strategic importance following a historic peace deal signed in December between the Colombian government and FARC rebels that is facing new challenges and allegations of noncompliance. Additionally, Colombia has important elections coming up next year.

Trump this week threatened that he would decertify Colombia as a partner in the war against drugs unless the South American nation reverses a record surge in cocaine production. Colombia is the source of 90 percent of the cocaine consumption in the U.S.

With Colombia’s ability to maintain the peace deal growing shakier each day, one conservative foreign-policy activist said putting a career politician with no loyalty to Trump and his agenda in such a critical foreign policy post is counterproductive.

"That someone thinks this is a good idea is quite disturbing," one conservative foreign-policy activist told the Free Beacon. "Tillerson has the potential to be a great secretary of state in the [John Foster] Dulles mold. He needs to recruit fresh, political ambassadors who can robustly advance President Trump’s vision for the Americas. MacManus is not the right fit."

The State Department referred questions about a MacManus appointment to the White House, which did not immediately respond to a request for comment.

A senior congressional aide warned that MacManus's nomination for the ambassadorship could face significant GOP hurdles in the Senate, especially after a clash he had with several conservative senators earlier this year.

"If they want to go down this route, it’s not going to be a smooth confirmation process," the aide warned.

Even though MacManus, who is currently serving as acting assistant secretary of State for legislative affairs, is well-liked among top State Department officials, he rubbed several conservative senators on Capitol Hill the wrong way earlier this year.

Conservatives on Capitol Hill and throughout Washington are questioning why career diplomats, especially those with close ties and relationships with Clinton, remain in key leadership roles and why some, such as MacManus, are under consideration for promotions in the Trump administration.

Back in April, MacManus angered six conservative senators by essentially rebuffing their request for an investigation into whether the State Department and the U.S. Agency for International Development were using taxpayer money to support liberal causes they viewed as having no clear national-security interest.

The senators, including GOP Sens. Mike Lee (Utah), Ted Cruz (Texas), Jim Inhofe (Okla.), Bill Cassidy (La.) and Thom Tillis (N.C.), specifically wanted a review into how USAID was working with groups funded by George Soros "to push a progressive agenda and invigorate the political left," the Heritage Foundation's Mike Gonzales wrote for the New York Post.

The senators cited several Soros-funded projects, including one in Colombia in which USAID funds support a Soros-owned media portal that has criticized Trump, capitalism, and "patriarchal society."

MacManus, in a written response to the senators, defended USAID’s work without responding to their concerns about U.S. tax dollars supporting Soros’s causes and their call for a State Department review into those funding decisions.

"The Department of State’s foreign assistance programs are rigorously designed, implemented and monitored to ensure that they are based on core American values," MacManus said in a letter.

At least some of the senators interpreted MacManus's response as a blow-off signaling that their request and oversight in general wasn’t welcome.

If Trump nominates MacManus to the ambassadorship, Republican senators also will undoubtedly grill him about his years working closely with Clinton, including the role he played in the aftermath of the Benghazi attacks and during Clinton’s email scandal.

MacManus served as Clinton’s executive assistant when she came to the State Department, a role that involved traveling with her and working closely with Cheryl Mills, Clinton’s long-time top aide and chief of staff at State, to help manage the professional office and its staff. He served in the same capacity for former Secretary of State Condoleezza Rice for six months in 2008 before the Bush administration ended.

He went on to become the principal deputy assistant secretary of State for legislative affairs from April 2011 to May 2012, then went back to serving as Clinton’s executive assistant for several months, including during the Benghazi attacks.

MacManus was one of three Clinton aides who knew it was a terrorist attack within minutes of it happening, according to emails Judicial Watch obtained from the State Department through a Freedom of Information Act lawsuit. It was MacManus who forwarded the news of Ambassador Christopher Stevens’ death to officials in the State Department Legislative Affairs Office with instructions not to "forward to anyone at this point."

Despite this knowledge given to her top staffers, Clinton still issued an official statement claiming the assault may have been in response to an inflammatory video posted on the Internet.

Three years later, MacManus was embroiled in Clinton’s email scandal, forced to make statements to a district judge that no one at State required Clinton to use a government cell phone and simply allowed her to conduct government business via a personal email account on a private server. Critics cited MacManus's sworn statements as proof that State Department officials acquiesced to Clinton’s unorthodox communications practices.

MacManus also suggested to the same judge that government-issued phones given to Clinton's top aides, Mills and Huma Abedin, had been destroyed because they were older models.

After President Barack Obama won reelection, MacManus was promoted to the plum post of U.S. permanent representative to the United Nations in Vienna and to the International Atomic Energy Agency, where he played a key role in trying to hold Iran accountable for its promises to curtail its nuclear activity.

At MacManus's nomination ceremony, Clinton heaped praise on MacManus and said his departure for such a key diplomatic post was bittersweet because she had built up such a trusting and enjoyable relationship with him.

"It was clear from the start that Joe is a special kind of person—calm, collected, [with] impeccable judgement, just the kind of person you want for the non-stop blur of activity that is our office," she said.

MacManus gave conservative foreign-policy hardliners something to cheer about in 2013.

During a tense moment with Iran, MacManus was one of several Western diplomats to storm out of a United Nations meeting to protest after the Iranian representative went on a lengthy tirade about Israel that included an accusation that it had a "dark record of genocide."

He went on to serve as Secretary of State John Kerry’s first choice to coordinate U.S. agencies' implementation of the Iran nuclear deal in mid-2015, but only for an interim period.