Republican Sens. Ted Cruz and Mike Lee are urging President Trump not to appoint as ambassador to Colombia 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 aftermath of the Benghazi attacks.

Joseph MacManus, a 30-year veteran of the foreign service, is a top candidate to become ambassador to Colombia and was considered the frontrunner before conservatives began voicing opposition to his nomination a few weeks ago, according to several GOP sources.

His nomination has the support of both Secretary of State Rex Tillerson and Tom Shannon, a career foreign service diplomat who serves in the State Department as undersecretary for political affairs and is considered Tillerson's right-hand man.

The two conservative senators this week expressed deep concern that MacManus was too close to Clinton during her tenure, doesn't share Trump's "America First" agenda and other conservative foreign-policy goals, and, as one of Clinton's closest advisers, was deeply involved in the State Department's initial response to the Benghazi attack.

Conservatives in Congress and the foreign-policy community argue that the role of ambassador to Colombia, Washington's staunchest ally in Latin America, is a critical one and any candidate for the post should have extensive experience in the region.

The U.S. diplomatic post in Bogota carries new strategic importance following a historic peace accord signed in December between the Colombian government and FARC rebels that is facing new challenges and allegations of noncompliance.

"At a time where the U.S.-Colombia partnership is so vital to our national-security interests, and after U.S. taxpayers have invested billions in security assistance for Colombia, it is deeply troubling that Secretary Clinton's top advisor—who played a key role in the Benghazi cover-up—might be placed in a position to significantly influence foreign-policy in Colombia, our only NATO partner in Latin America," Cruz, a Republican from Texas, said.

"The Senate should scrutinize this nomination closely," he added.

Lee, a Republican from Utah, was equally concerned about the possibility of a MacManus appointment.

"While Mr. MacManus has a career of service in the State Department, it is concerning that the Trump administration is considering nominating ambassadors that do not share the conservative values of the American people who voted for President Trump, and in this case, who helped then-Secretary Clinton clean up her Benghazi mess," Lee told the Washington Free Beacon.

The comments from Cruz and Lee suggest MacManus will likely face a nasty confirmation battle that will touch on the role he played as Clinton's top aide in the immediate aftermath of the Benghazi attack, as well as during the scandal over her use of a private email account while serving as secretary of State.

The State Department did not immediately respond to the concerns expressed by Cruz and Lee about a MacManus appointment. However, State's press secretary Heather Nauert defended MacManus's qualifications for an ambassadorship in mid-September.

"Secretary Tillerson does not agree that career ambassadors lack the vision to solve tough problems," she said in an emailed statement. "MacManus is highly respected for his leadership, collegiality, and professionalism. He has served his country in challenging posts across multiple administrations and has demonstrated his exceptional leadership."

"MacManus was sworn into office under President Ronald Reagan," she added.

Some members of the conservative foreign-policy community in Washington argue that the Colombia ambassadorship should become a political appointment, not one in which only career foreign service officers are considered.

They point to a memo penned and circulated during the Trump presidential transition period last fall. Titled "Talking Points Embassy of U.S. in Colombia as Political Post for Ambassadorship," the memo advised Trump not to choose a career diplomat to lead the embassy in Bogota.

Instead, the memo said the post should only go to a candidate who is not worried about his next job at State and can forcefully carry out Trump's foreign-policy goals there.

The memo points out that, in the past, State Department-led "bureaucrats cut off U.S. military aid to the police in Colombia as the GOP Congress fought to save Colombia from the FARC terrorist threat, while simultaneously tacking the drug threat."

"Without this type of political support, military aid, and supportive push from a GOP Congress in the 1990s, it might have become a failed nation and even greater ‘narco-state' threat to the U.S."

"We can't take that chance again," the memo states.

The GOP senators' concerns about MacManus's time serving as one of Clinton's closest aides stems from reports that he was one of three of her aides who knew Benghazi was a terrorist attack within minutes of it happening.

Emails obtained by Judicial Watch from the State Department through a Freedom of Information Act lawsuit show that MacManus forwarded the news of Ambassador Christopher Stevens's death to the official in the State Department Legislative Affairs Office with instructions not to "forward to anyone at this point."

Conservatives have expressed outrage that Clinton still issued an official statement claiming the assault may have been in response to an inflammatory video posted on the Internet even though she and her top aides quickly knew it was a terrorist attack.

The senators also are likely to question MacManus on whether he played any role in allowing Clinton to conduct government business via a personal email account on a private server and did not force her to use a government-issued cell phone.

MacManus was forced to make statements to a district judge that no one at State required Clinton to use a government cell phone.

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

Cruz and Lee also were among a group of six senators angered by MacManus's response to 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.

Cruz and Lee, along with 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 Gonzalez 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 brush-off signaling that their request and oversight in general wasn't welcome.