Former Trump physician Navy Rear Adm. Ronny Jackson running for Texas congressional seat

Jackson resigned from the White House on Dec. 1, according to a spokesperson.

Navy Rear Adm. Ronny Jackson, the former presidential physician and one-time veterans affairs secretary pick, is running in the Republican primary for Texas' 13th Congressional District, according to the Texas Republican Party.

Filing on the last day to do so, Jackson is joining a crowded primary field. There are at least 14 candidates are vying for the Republican nomination for the seat currently held by Rep. Mac Thornberry, the ranking member of the House Armed Services Committee, according to the state party. Thornberry announced at the end of July that he would not seek re-election for the district he's represented since 1995.

Jackson resigned from his job at White House on Dec. 1, White House deputy press secretary Judd Deere told ABC News. At the time of his resignation, Jackson served as an assistant to the president and chief medical adviser, a newly created position that he took on in February.

Instead of providing medical care at the White House, in this last role, Jackson gave "technical policy advice" on public health issues, including veterans' issues and the opioid epidemic, an administration official who is not authorized to speak publicly told ABC News after Jackson's promotion.

Before he held that job, Jackson served as the doctor to Presidents George W. Bush, Barack Obama and Donald Trump. While he remained in the White House medical unit, he gave up his job as presidential physician when Trump tapped him in March 2018 to serve as secretary to the Veterans Affairs Department. Dr. Sean Conley, a Navy officer, took over the job, and is still Trump's doctor.

The Senate never voted on Jackson's nomination to be veterans affairs secretary. After facing allegations of misconduct, including improperly dispensing medications, wrecking a government vehicle after drinking and mistreatment of White House colleagues, Jackson withdrew his name from consideration in late April 2018.

He denied the allegations in a statement at the time, saying they were "completely false and fabricated."

Those allegations are still under investigation by the Department of Defense Office of Inspector General, spokeswoman Dwrena Allen said on Monday.

When he withdrew his name, Trump continued to back Jackson, saying in an interview on Fox News that the Navy doctor would've been great, and maintained that the allegations were false, saying, "They are trying to destroy a man."

In January 2018, after the president's first physical exam since taking office, Jackson found himself in the spotlight, giving a glowing review of Trump's health.

Jackson told reporters in a White House press briefing after the physical that Trump "has incredibly good genes."

"I told the president that if he had a healthier diet over the last 20 years, he might live to be 200 years old. I don't know," he said at the time.

ABC News' Ben Gittleson and Luis Martinez contributed to this report.