Trump's national field director resigns

Republican front-runner Donald Trump's national field director has resigned amid major changes to the campaign's top leadership.

Stuart Jolly, 52, said in an interview on Monday night that he decided the time had come for him to leave the campaign.

He resigned in a letter on Monday where he thanked the business mogul for hiring him, even though he had never worked on a national campaign before, The Washington Post reported.

"As your National Field Director, my guidance to the states' staff and strike teams was to always to focus, keep moving, grow the base, love on your volunteers, and take care of your people," Jolly wrote in the letter, which he shared with The Washington Post.

"We did these simple things, we won, and we continued to win because we followed a winning formula. You know my advice to you, and my advice has not changed since the beginning."

"My hope is that you will continue to listen to those who have propelled you to victory," he added.

According to the letter, as Trump's chances of locking up the Republican nomination before the convention in July have faded, Lewandowski saw his role in the campaign lessened.