A handful of prominent former Trump administration officials are backing President Trump Donald John TrumpFederal prosecutor speaks out, says Barr 'has brought shame' on Justice Dept. Former Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick MORE's pick to be the next ambassador to Russia, John Sullivan, in a letter ahead of his confirmation hearing.

The letter signed by figures such as former Ambassador to the United Nations Nikki Haley Nimrata (Nikki) Haley'The soul' versus 'law and order' Author Ryan Girdusky: RNC worked best when highlighting 'regular people' as opposed to 'standard Republicans' GOP lobbyists pleasantly surprised by Republican convention MORE and former Defense Secretary James Mattis James Norman MattisBiden courts veterans amid fallout from Trump military controversies Trump says he wanted to take out Syria's Assad but Mattis opposed it Gary Cohn: 'I haven't made up my mind' on vote for president in November MORE comes on the eve of Sullivan's confirmation hearing before the Senate Foreign Relations Committee.

Sullivan, who currently serves as deputy secretary of State, is praised in the letter as "the right person at the right time" for the job. In addition to Haley and Mattis, the letter was signed by former national security adviser H.R. McMaster and former acting Secretary of State Tom Shannon.

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The letter was sent to Foreign Relations Committee Chairman Jim Risch James (Jim) Elroy RischWhy the US should rely more on strategy, not sanctions Davis: The Hall of Shame for GOP senators who remain silent on Donald Trump Senators blast Turkey's move to convert Hagia Sophia back into a mosque MORE (R-Idaho) and ranking member Sen. Bob Menendez Robert (Bob) MenendezWatchdog confirms State Dept. canceled award for journalist who criticized Trump Kasie Hunt to host lead-in show for MSNBC's 'Morning Joe' Senators ask for removal of tariffs on EU food, wine, spirits: report MORE (R-N.J.), according to a person familiar with the document.

Sullivan joined the administration in 2017. He was confirmed to be deputy secretary of State by a 94-6 vote. If confirmed as the top U.S. diplomat to Moscow, he will replace Jon Huntsman, who served in the role for roughly two years.

Bloomberg first reported on the letter in support of Sullivan.

The Russia ambassador role has become particularly scrutinized during the Trump administration amid heightened tensions between Washington and Moscow.

Trump has faced intense criticism for speaking favorably about Russia, and his campaign's interactions with Russian figures were a major focus throughout special counsel Robert Mueller Robert (Bob) MuellerCNN's Toobin warns McCabe is in 'perilous condition' with emboldened Trump CNN anchor rips Trump over Stone while evoking Clinton-Lynch tarmac meeting The Hill's 12:30 Report: New Hampshire fallout MORE's investigation into Russian interference in the 2016 election.

Adding another layer to the complex dynamic involving U.S. policy toward Russia is allegations that Trump earlier this year pressured the leader of neighboring Ukraine to launch investigations into Trump's political rivals.

Acting White House chief of staff Mick Mulvaney Mick MulvaneyOn The Money: House panel pulls Powell into partisan battles | New York considers hiking taxes on the rich | Treasury: Trump's payroll tax deferral won't hurt Social Security Blockchain trade group names Mick Mulvaney to board Mick Mulvaney to start hedge fund MORE told reporters earlier this month that military aid for Ukraine intended to combat Russian aggression was tied in part to the Ukrainians agreeing to investigate Democrats in the 2016 election.

Sullivan will likely be asked about the controversy, particularly since he was the official who was tasked with dismissing former U.S. Ambassador to Ukraine Marie Yovanovitch at Trump's request.

Yovanovitch testified earlier this month in the House impeachment inquiry that she felt she was the target of misinformation being spread by President Trump's allies.