Democratic presidential candidate Hillary Clinton has already instructed her attorney to hand over her private email server and a thumb drive containing all her work-related emails to the Justice Department to quell controversy surrounding her otherwise smooth slide to the Democratic nomination, U.S. TV network CNN said on Tuesday.

Quoting Clinton's spokesman Nick Merrill, CNN reported that the undisputable Democratic presidential front-runner has "directed her team to give her email server" which was exclusively during her years as the top U.S. diplomat, to Justice Department as well as a thumb drive with all her work-related emails.

For months, Republican rivals, including House speaker John Boehner, had called for the Clinton camp to hand over to authorities her private email server but to little avail, and the voluntary handing over by the Clinton camp this time indicated the Clinton camp's increasing concern that the issue could further dent Clinton's trustworthiness.

Though starting with a strong momentum, favorability rating for Clinton dipped recently as the former Secretary of State was grappling with negative news coverage, including her controversial practice of exclusively using personal email account and server while working as the U.S. top diplomat.

According to the latest Quinnipiac poll released on July 30, 57 percent of voters regarded Clinton as not honest and trustworthy. Other national polls also indicated that an increasing number of Americans see Clinton as not honest as the leader of the country.