President Trump re-nominated his former physician Rear Adm Ronny Jackson (above) to be promoted to a two-star admiral in a letter to the Senate on January 15 despite an ongoing Pentagon investigation into allegations of impropriety

President Donald Trump has re-nominated his former physician Rear Adm Ronny Jackson to be promoted to a two-star admiral despite the ongoing Pentagon investigation into allegations of impropriety.

The White House sent a letter to the Senate requesting Jackson's bump in military rank on January 15, according to The Washington Post.

Jackson withdrew from consideration as Trump's nominee for secretary of Veterans Affairs last year after allegations emerged that he was 'abusive' toward colleagues, allowed the over-prescribing of pain medications and was periodically intoxicated on the job.

The US Navy admiral categorically denied all of those allegations, calling them 'completely false and fabricated'.

However, the Senate Armed Services Committee is not expected to consider the nomination until the investigation by the Defense Department's Inspector General's Office is completed, according to two Senate aides.

'The White House is the one who resubmitted his nomination to the Senate and so we'll see -- there's an investigation going on, that's in progress so all of these things have to kind of culminate to see where we go,' Adm John Richardson, the chief of naval operations, told CNN.

Jackson withdrew from consideration as Trump's nominee for secretary of Veterans Affairs last April after the accusations from his colleagues emerged. The US Navy admiral (above with the president in January 2018) has denied all allegations

A Navy official said Trump nominated Jackson for a second star without a recommendation from a military promotion board, which is atypical, though President Barack Obama also did not rely on a board when nominating Jackson for his first star in 2016.

'While promotion boards are typically used to recommend officers for Presidential appointment to the grade of rear admiral, the Constitution does not require that a Board be used,' the official told CNN.

Richardson confirmed Jackson is currently working in the White House medical unit, but said he did not know what his day-to-day duties involve.

He reportedly no longer attends to the president, after having served in that role since 2006.

Jackson was ridiculed last January after he delivered a glowing assessment of the president's health during a routine briefing on his physical exam - despite test results indicating that Trump is borderline obese and has a common form of heart disease.

The admiral joked that if Trump had a 'healthier diet over the last 20 years, he might live to be 200 years old'.

Trump picked Jackson to lead the Veterans Affairs Department three months later, but the physician withdrew his name from consideration after Sen Jon Tester, the Veterans' Affairs Committee's ranking Democrat, publicly released a collection of allegations against him.

The committee said 23 current and former colleagues had come forward to accuse Jackson of prescribing himself medications, getting drunk at a Secret Service party and wrecking a government vehicle.

He was also accused of over-prescribing sleeping pills, drinking while on duty and fostering over a hostile work environment.

A Navy official said Trump nominated Jackson for a second star without a recommendation from a military promotion board