Republican US presidential nominee Donald Trump holds a campaign rally at the ?Ziegler Building at the Washington County Fair Park & Conference Center in West Bend, Wisconsin August 16, 2016. [Photo/Agencies]

WASHINGTON - US Republican presidential candidate Donald Trump moved on Wednesday to overhaul his struggling campaign, tapping a seasoned political operative and the head of the conservative website Breitbart News for top roles.

Trump named veteran political strategist Kellyanne Conway his campaign manager, and Breitbart News executive chairman Stephen Bannon has been brought on as the campaign's chief executive, the Trump campaign said in a statement.

The shakeup comes as opinion polls show Trump, a wealthy New York businessman who has never held elected office, falling behind Democratic candidate Hillary Clinton in the race for the Nov. 8 election.