Sen. John McCain John Sidney McCainMomentum growing among Republicans for Supreme Court vote before Election Day McConnell urges GOP senators to 'keep your powder dry' on Supreme Court vacancy McSally says current Senate should vote on Trump nominee MORE (R-Ariz.) urged Secretary of State Rex Tillerson Rex Wayne TillersonGary Cohn: 'I haven't made up my mind' on vote for president in November Kushner says 'Alice in Wonderland' describes Trump presidency: Woodward book Conspicuous by their absence from the Republican Convention MORE on Wednesday to end his hiring freeze in the State Department, citing concerns that a depletion of foreign service officers could harm U.S. diplomatic efforts.

McCain and Sen. Jeanne Shaheen Cynthia (Jeanne) Jeanne ShaheenSenate Democrats introduce bill to sanction Russians over Taliban bounties Trump-backed candidate wins NH GOP Senate primary to take on Shaheen Democratic senator urges Trump to respond to Russian aggression MORE (D-N.H.) wrote a joint letter to Tillerson taking issue with the department's "failure to replace losses" in its ranks "due to attrition and resignations," that they said appeared as if intentionally aimed at reducing the department's staff size.

"We know from experience that shutting off the intake of entry-level Foreign Service officers will inevitably result in shortages of appropriately experienced personnel at specific grades in future years," the senators wrote.

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The senators demanded that the State Department lift the freeze, refrain from imposing any further measures aimed at reducing staffing levels and promote high-performing officers to retain talent in the department.

McCain and Shaheen cited the drastic numbers of departures from the department and falling numbers of entry-level applicants, which they said were the product of "questionable management practices" and a "lack of experienced leadership."

Tillerson in April decided to maintain the hiring freeze even as other federal agencies lift their freeze.