(CNN) Amid escalating tensions at the US-Mexico border, there is currently no ambassador or even a nominee to the key diplomatic post in Mexico City -- one of more than a dozen that is vacant and without a nominee.
The Senate Foreign Relations Committee will consider 18 nominations during a business meeting Wednesday in the wake of a standoff Sunday between US border officials and a group of migrants, in which a major border crossing was temporarily closed and US Border Patrol agents fired tear gas at a group of migrants.
The top diplomatic posts in Saudi Arabia, Turkey and Yemen also remain unfilled as the US grapples with continued fallout from the murder of Jamal Khashoggi and the military and humanitarian implications of the conflict in Yemen.
There are 68 ambassadorial vacancies, not including international organizations, according to a tracker from the American Foreign Service Association (AFSA). Of those, 49 have nominees and six nations do not exchange ambassadors with the US.
"We remain dedicated to filling critical posts around the globe with ambassadorial candidates who are most qualified to advance US leadership and America's foreign policy priorities abroad. We will continue to work with the Senate to confirm these qualified, solid nominees, before the end of the year so that these candidates may take their place alongside the finest diplomats in the world," State Department spokesperson Heather Nauert said.
There is no ambassador or nominee for ambassador to Mexico, but Secretary of State Mike Pompeo and other officials have been in communication with their Mexican counterparts on the migrant issue, according to the State Department.
The post for US ambassador to Saudi Arabia is vacant, with nominee John Abizaid being named only weeks ago. The Charges d'Affaires at the US Embassy in Riyadh Christopher Henzel -- who leads the embassy in the absence of an ambassador -- has been nominated to an ambassador role in Yemen. Turkey has no nominee for its vacancy.
Pressed about these particular vacancies in mid-October, State Department deputy spokesperson Robert Palladino noted that there were senior diplomatic staff at the helms of the embassies.
"These are senior Foreign Service officers that have had full careers and we're confident in our team's ability," he said.
Ambassador Ronald Neumann, a former US ambassador to Algeria, Bahrain and Afghanistan and the president of the American Academy of Diplomacy, said the importance of having an ambassador installed depends on the country. In countries where the US does not have deep relations, the role of the ambassador is critical, Neumann told CNN.
"The ambassadors always have an easier time reaching a higher level of the host government," he said, who noted that it is harder for the second in command to gain the same level of access. "You get the job done but more slowly."
Moreover, as the President's representative, it is the ambassador's role to keep the many officials from various branches of government in line, Neumann said.
"The ambassador has to keep them from going off on all different agency directions," he explained.
For Neumann, it is the delay in filling top positions at the State Department and what he sees as the "disinclination of this administration to make use of career officials" that are a bigger cause for concern.
"I think this is an administration that does not trust a career service of any kind," he said, warning of destroying "the nonpolitical meritocracy of our professional US government."
"If you're not careful, you'll be back to the spoils system of the 1900s," Neuman said.
According to AFSA's tracker, Trump's ambassadorial nominees are almost evenly split between career and political appointments. However, his appointments to senior State Department positions have been 90% political.
In a charged October statement, Secretary of State Mike Pompeo sought to blame Congress for the gaps in staffing both abroad and in Foggy Bottom. However, the State Department has expressed approval at the pace of confirmations in the passing month.
"Since October we've made progress with Senate confirmations. We were pleased that the Senate confirmed eight nominees before they recessed for the midterm elections. These confirmations included our Assistant Secretary for Western Hemisphere Affairs Kim Breier and our Assistant Secretary for Conflict and Stabilization Operations, Denise Natali. In addition, we welcomed Mary Elizabeth Taylor, our Assistant Secretary for Legislative Affairs, who is spearheading the Senate confirmation process for our nominees. We still have approximately 70 nominees pending before the Senate and are working hard to confirm them before the end of the year," Nauert said.
Questions have been raised about some of Trump's ambassadorial nominees. For example, a CNN KFile review found that his choice for ambassador to Barbados and several other Caribbean countries spread fringe conspiracy theories and unfounded attacks about Trump's political opponents on Twitter, including ones about Sen. Ted Cruz and his wife, Heidi, during the 2016 presidential election.
Former deputy national security adviser KT McFarland withdrew her nomination to be US ambassador to Singapore in February. In December, Democrats placed a hold on the nomination until she answered their questions about her knowledge of communications between fired national security adviser Michael Flynn and then-Russian Ambassador to the US Sergey Kislyak, a Democratic source told CNN at the time.