President Trump called on Montana's Sen. Jon Tester to resign over the Democrat's role in surfacing unproven misconduct allegations that prompted the president's pick to run the Department of Veterans Affairs, Ronny Jackson, to withdraw his name Thursday. Mr. Trump said Tester — who faces a tough election in November in a state where Mr. Trump's approval rating is among the highest — "should resign."

Tester said he had compiled accusations against Jackson based on more than 20 current and former military members. The allegations included excessive drinking on the job and improperly dispensing medications.

"Allegations made by Senator Jon Tester against Admiral/Doctor Ron Jackson are proving false," Mr. Trump tweeted Saturday. "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."

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Tester faces a tough race in November — his Republican challenger will be determined by a June primary — in a state where Mr. Trump enjoys a 52 percent approval rating as of January, according to Gallup.

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

"The great people of Montana will not stand for this kind of slander when talking of a great human being," President Trump continued Saturday in a tweet. "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!"

....great people of Montana will not stand for this kind of slander when talking of a great human being. 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! — Donald J. Trump (@realDonaldTrump) April 28, 2018

Later in the day, after a trip to his golf club in Northern Virginia, the president said he had just been informed that the statements about Jackson were untrue from the Secret Service, although it's unclear exactly what he meant by that. The Secret Service could not immediately be reached for comment Saturday afternoon.

Secret Service has just informed me that Senator Jon Tester’s statements on Admiral Jackson are not true. There were no such findings. A horrible thing that we in D.C. must live with, just like phony Russian Collusion. Tester should lose race in Montana. Very dishonest and sick! — Donald J. Trump (@realDonaldTrump) April 28, 2018

On Saturday, Tester responded to Mr. Trump's call for his resignation by saying he has a duty to ensure veterans in his state get what they've earned.

"I'll never stop fighting for them," Tester said in a statement.

The White House had already taken issue with allegations against Jackson, saying Friday that internal records raise doubt about some of the most serious allegations leveled against Jackson. One allegation was that once, at a Secret Service going away party, "Jackson got drunk and wrecked a government vehicle," according to a summary of accusations compiled by Democrats on the Senate Veterans' Affairs Committee.

Internal records, including police reports, show that Jackson was in three minor vehicle incidents in government vehicles during the last five years, but none involved the use of alcohol and he was not found to be at fault. In one case, a side-view mirror was clipped by a passing truck. In another incident an enraged driver in Montgomery County, Maryland, allegedly punched out Jackson's window during a morning drive to Camp David.

The White House medical unit that Jackson ran successfully passed regular controlled substance audits, according to the records for the last three years. The reviews did recommend improvements to the medical unit's handling of controlled substances, but did not find misconduct.

The Associated Press reviewed the documents Friday. They were the result of an internal White House review of allegations raised against Jackson during his brief confirmation process. The White House says the records, covering recent years, disprove the allegations.

But Tester's office has not specified the time frame during which the alleged misconduct occurred. Tester spokeswoman Marnee Banks told the AP the office would not comment until it knew more about the White House records.

Separately, the Secret Service said it has no evidence to support an allegation that its personnel intervened to prevent Jackson from disturbing former President Barack Obama during a foreign trip in 2015.

In a statement dated Thursday, the Secret Service said it had conducted a "thorough review" of internal documents related to Obama's foreign trips in 2015 and interviewed people who were present. The agency said it has found "no information that would indicate the allegation is accurate" and no record of any incident involving Jackson. CNN had reported allegations that Jackson drunkenly banged on the hotel room door of a female employee and that Secret Service personnel intervened out of concern that he would wake Obama.

Jackson has denied the accusations, calling them "baseless and anonymous attacks" on his character and integrity that are "completely false and fabricated."