In Tester's report, 23 military colleagues say that Jackson would prescribe drugs "like candy" without paperwork or examinations, while also writing himself prescriptions and pressuring others to recklessly hand out sleeping pills.
Gidley said the FBI background investigation into Jackson "was clean and there are no issues in the background check whatsoever".
Veterans' Affairs Committee Chairman Johnny Isakson, R-Ga., and Tester sent a letter to Trump on Tuesday requesting additional documentation related to Jackson's tenure as the president's doctor and his role leading the White House medical team.
Jackson's nomination came following the removal of David Shulkin from heading the VA, but his confirmation is in jeopardy as Democrats and Republicans on the Senate Veterans' Affairs Committee review allegations against him.
"Dr. Jackson deserves a fair hearing and we are not going to write him off in any way before his hearing, and quite frankly neither should members of Congress", White House spokesman Hogan Gidley told Rachel Martin on NPR's Morning Edition Wednesday. Trump said he told Jackson Tuesday.
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The hearing was set to take place this week, but it was delayed due to the allegations.
Jackson, 50, has served as director of the White House Medical Unit since 2011 and as physician to the president since 2013. "I can only speak to some of the personal accounts that those of us have, as well as the records that we have that are substantiated through a very detailed and thorough background investigation process". Jackson served in the Navy as a rear admiral. "In fact, because Dr. Jackson has worked within arm's reach of three presidents, he has received more vetting than most nominees".
"I had questions at the outset about whether he had the management experience", Mr. Coons said when asked if he thought the accusations were part of a "smear campaign".
"If you are drunk and something happens with the president, it's very hard to go in and treat the president", Tester said.
Senate staff did not include the names or other identifying information of the people making the allegations.