A supporter and former close adviser to Senator Rand Paul has been charged with hiding secret payments to secure the endorsement of an Iowa lawmaker during the 2012 presidential campaign of the senator’s father, former Representative Ron Paul, the Justice Department said on Wednesday.

Jesse Benton, who was Ron Paul’s presidential campaign manager, is accused of paying more than $70,000 to Kent Sorenson, a former Iowa state senator, to win his support before the state’s caucuses in 2012. Mr. Sorenson had been backing Representative Michele Bachmann at the time but later switched to support Mr. Paul.

The charges against Mr. Benton are the latest blow to Rand Paul’s campaign, which has struggled to gain traction in the polls and has had fund-raising troubles and staff turmoil.

Mr. Benton had been tapped to run America’s Liberty, a “super PAC” that supports the younger Mr. Paul’s presidential bid. Also charged are John Tate and Dimitrios Kesari, who worked with Mr. Benton on the 2012 campaign.