The detail is one of the many insights into the Republican candidate's campaign given in an article in the New York magazine in its latest edition.
"Several months ago, he began wearing a bulletproof vest," the magazine said citing two sources close to the campaign.
"People who know Trump say they've never seen him so tired. Several months ago, he began wearing a bulletproof vest...Which has added to his discomfort on the stump, leaving him sweaty and spent after events," the article on Trump says.
Trump is currently leading the delegate count but has been under fire recently for his comments on abortion.
However, Trump is the only Republican with a realistic path to clinching the nomination ahead of the Republican convention but a big loss in Wisconsin would greatly reduce his chances of reaching the needed 1,237 delegates before then.