President Donald Trump criticized Sen. Jon Tester of Montana for smearing White House physician Ronny Jackson after the president nominated him to serve as secretary of Veterans Affairs.

“The Secret Service is unable to confirm (in fact they deny) any of the phony Democrat charges which have absolutely devastated the wonderful Jackson family,” Trump wrote on Twitter. “Tester should resign.”

In a statement, the Secret Service said it had no evidence of any incident with Dr. Jackson, despite two pages of unproven allegations published by Tester about his behavior at the White House.

Jackson withdrew his name from consideration for Veterans Affairs on Thursday, despite denying the accusations.

Trump has since accused Tester of unfairly and falsely smearing a good man, as the Montana senator is running for re-election in the fall.

“The great people of Montana will not stand for this kind of slander when talking of a great human being,” Trump wrote. “Admiral Jackson is the kind of man that those in Montana would most respect and admire, and now, for no reason whatsoever, his reputation has been shattered. Not fair, Tester!”

Allegations made by Senator Jon Tester against Admiral/Doctor Ron Jackson are proving false. The Secret Service is unable to confirm (in fact they deny) any of the phony Democrat charges which have absolutely devastated the wonderful Jackson family. Tester should resign. The….. — Donald J. Trump (@realDonaldTrump) April 28, 2018