WASHINGTON (Reuters) - U.S. Treasury Secretary Steven Mnuchin said on Sunday he does not regret using a government plane to travel to Kentucky in August with his wife to view the solar eclipse and speak to business leaders, calling it “completely justifiable.” Mnuchin’s use of the plane at taxpayers’ expense prompted an outcry from Democratic lawmakers and interest groups and spurred a government watchdog to begin examining whether it violated travel or ethics policies.  “It was approved by the White House and there were reasons why we needed to use that plane that are completely justifiable,” he said on NBC’s “Meet the Press” program. Cabinet members rarely use government planes or chartered aircraft for domestic travel, but the practice has received significant attention in the wake of Mnuchin’s trip. On Friday, former Health and Human Services Secretary Tom Price resigned after an outcry over his use of private charter planes for government business at a cost of nearly $52,000.  Mnuchin told NBC that he would only use a private plane for government purposes “if either there was a national security issue or we couldn’t get somewhere.” The Treasury Department has described Mnuchin’s trip in August as official government travel. Mnuchin spoke to business leaders in Louisville and visited Fort Knox, the site of significant U.S. gold reserves. Mnuchin and his wife, Louise Linton, also viewed the Aug. 21 solar eclipse in Kentucky with Senate Majority Leader Mitch McConnell and others.  Public uproar over the trip began to mount after Linton posted a photo of herself deboarding the plane on social media and listed the expensive designer brands she was wearing in the caption. 