The Secret Service is disputing the allegation, first reported by CNN, that on an overseas trip in 2015 Jackson drunkenly banged on the door of a female colleague so loudly that Secret Service agents had to calm him down so as to not disturb President Barack Obama.
"Over the last 48 hours, media outlets have alleged that U.S. Secret Service personnel were forced to intervene during a Presidential foreign travel assignment in order to prevent disturbing (former) President Barack Obama. The Secret Service has no such record of any incident; specifically, any incident involving Rear Admiral Ronny Jackson," the Secret Service said in a statement.
The law enforcement agency said it performed a thorough review of internal documents related to all of President Obama's foreign travel in 2015 and interviewed personnel who were present during those trips. The investigation turned up no information that indicated the allegation is accurate, according to the statement.
"Look I don't want to get into specifics, but I can tell you there is a pattern of behavior here and several different episodes that would indicate we need to find out what the truth is and get to the bottom of it," Tester said in an interview with ABC News.
His office declined to comment on the Secret Service statement.
Jackson's confirmation hearing was postponed indefinitely earlier this week as multiple allegations against Jackson came to light.
In the most detailed account of allegations against Jackson so far, a document provided by Tester's office says the former VA secretary nominee improperly dispensed medications to others and himself, according to interviews with colleagues and former colleagues, who described him as unethical.
One of the allegations is that Jackson once got drunk and “wrecked” a government car.
Shortly after the document was released, Jackson denied several of the allegations when presented with them by reporters.
The document is based on interviews Democratic committee staffers did with 23 colleagues and former colleagues of Jackson’s, most of whom, Tester's office says, are still in uniform. The colleagues are cited as describing Jackson as “the most unethical person I have ever worked with,” “100 percent bad temper,” “the worst officer I have ever served with,” someone who would “lose his mind over small things,” “vindictive” and “belittling.”
One staffer at the White House Medical Unit was quoted in the documents as saying working there was the “worst experience of my life.”
The two-page list provided by Democrats is divided into three sections, including one titled “Drunkenness,” which alleges that on at least one occasion during an overseas presidential trip, Jackson could not be reached when needed, while he was "on duty," because he was passed out drunk in his hotel room.
The document also includes an allegation that “At a Secret Service going away party, Jackson got drunk and wrecked a government vehicle.”
The document says, as Tester had said Tuesday in interviews, that Jackson was known as the “Candyman” because he would provide prescriptions without paperwork.
Speaking at the White House just after the document was circulated, Jackson told a group of reporters in the halls of the West Wing that he has “never wrecked a car” and has “no idea” where the allegations about his practice of dispensing drugs are coming from.
White House press secretary Sarah Sanders defended Jackson Wednesday, saying no previous background checks for Jackson’s employment as the presidential physician raised any areas of concern, including one check conducted by the FBI. She defended his record as “impeccable.”
On Friday, Trump lamented Jackson's treatment during the nomination process.
"Ronny Jackson – admiral, doctor – is one of the finest men in a long period of time," Trump said at a news conference.
"To call him names to me was an absolute disgrace… I called him today: In a big way, you’re an American hero. You’ve exposed a system," Trump said.
The Secret Service is defending Jackson's record, too.
"Rear Admiral Jackson, in his role as the official White House Physician, has provided years of dedicated support to the men and women of the Secret Service, often miles from home and under difficult travel conditions, in order to ensure our personnel are healthy and prepared to execute our critical mission," the statement reads. "The Secret Service is grateful for the dedicated and outstanding professional service Rear Admiral Jackson has provided to the agency - and more importantly - his role supporting the greater Presidential protection security apparatus."
ABC News' Ali Rogin contributed to this story.