Senate Minority Whip Dick Durbin Richard (Dick) Joseph DurbinTumultuous court battle upends fight for Senate McConnell focuses on confirming judicial nominees with COVID-19 talks stalled Senate Republicans signal openness to working with Biden MORE (D-Ill.) is stepping up his call for an investigation into President Trump's former special assistant Sebastian Gorka's alleged ties to a neo-Nazis.

"Sebastian Gorka should never have been an advisor to POTUS. He should still be investigated for concealing neo-nazi ties," Durbin said in a tweet on Saturday, just one day after Gorka left his White House post.

.@SebGorka should never have been an advisor to @POTUS. He should still be investigated for concealing neo-nazi ties. https://t.co/6JzDJJ7UlY — Senator Dick Durbin (@SenatorDurbin) August 26, 2017

Gorka's departure from the White House was announced late Friday.

Durbin, along with Sen. Richard Blumenthal (D-Conn.) and Sen. Ben Cardin Benjamin (Ben) Louis CardinCongress must finish work on popular conservation bill before time runs out PPP application window closes after coronavirus talks deadlock Congress eyes tighter restrictions on next round of small business help MORE (D-Md.) penned a letter to the Justice Department and Department of Homeland Security on Monday, prior to Gorka's resignation, pressing the government to investigate Gorka's alleged ties to a group the U.S. State Department has said "was under the direction of the Nazi Government of Germany."

Gorka came under fire after he was seen wearing a medal from the Hungarian order Vitezi Rend, which was founded by an ally of Adolf Hitler.

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He has claimed that the medal was awarded to his father for fighting communism in Hungary.

“As a senior counterterrorism advisor, Mr. Gorka is in a position of great importance and public trust. The American people are entitled to know if a senior White House official is under criminal investigation,” the three senators wrote in the letter.

The senators also acknowledged Gorka's reported failure to obtain a security clearance.

Gorka has a background in counterterrorism, however his role in the White House was never detailed in public.

“We are also concerned that, according to numerous media reports, Mr. Gorka has been unable to obtain a security clearance, which could be a result of an ongoing criminal investigation. It is unclear how Mr. Gorka can effectively advise the president on counterterrorism and other national security matters without a security clearance," the letter continued.