The Green Party presidential candidate has described the flooding in the US state of Louisiana as "a crisis of climate change".
Dr Jill Stein spoke as she surveyed the wreckage from the disaster, which has killed at least 13 people and displaced thousands more.
A week on, more than 2,800 people remain in shelters unable to return to their wrecked homes.
Republican presidential nominee Donald Trump also visited this week.
President Barack Obama has been criticised for not breaking off his holiday last week but he will come on Tuesday.
Dr Stein stood in front of a home gutted by the rains in Denham Springs to deliver her message on global warming.
"We see the Louisiana flood as further evidence of the global crisis posed by climate change," the Green Party released in a statement.
"Until we humans make global sweeping changes to our economic and social systems, we must expect these types of disasters to continue regularly."
Donald Trump, who has repeatedly called climate change a "hoax," helped volunteers unload aid supplies from the back of truck near the town of Baton Rouge.
Surrounded by members of the media and a small gathering of locals, he attended church and gave encouragement to people he met.
"You're going to rebuild," he said to one passer-by. "It's going to be so beautiful."
Hillary Clinton, the Democratic nominee, has taken to Facebook to voice her sympathy for victims.
"My heart breaks for Louisiana," she said in a statement. She has declined to visit the area to avoid disrupting relief efforts, she said.
The difficult process of rebuilding flooded homes is only just beginning, as waters continue to recede.
Disaster relief centres have been set up in the towns of Baton Rouge, Amite and St Francisville.
Tens of thousands of people are looking for housing, after more than 40,000 homes were damaged.