Paul Manafort, campaign chairman for Republican presidential nominee Donald Trump, has resigned just two months after taking the helm.
He has come under fire for his ties to Russian interests and former Ukrainian President Viktor Yanukovych.
But he has denied any wrongdoing and it is not yet clear why he left.
The team was overhauled earlier this week with the addition of a new campaign chief executive and a new campaign manager.
Mr Trump, who arrived in Louisiana on Friday to meet flood victims, has come under pressure in recent weeks after a series of controversial remarks and falling poll numbers. READ MORE OF THIS MORE OF THIS REPORT
SOURCES: BBC NEWS