Bernie Sanders has backed legislation that would let Americans sue Saudi Arabia over the 9/11 terrorist attacks.
The bill is opposed by the Obama administration, but it is important to victims' families, some of whom believe Saudi officials played some part in the attacks.
The Democratic presidential candidate spoke in favour of the legislation on NBC's "Today Show" ahead of the New York presidential primary.
He said it was important to have a full understanding of the "the possible role of the Saudi government in 9/11."
US inquiries have not reported a link between the Saudi government or its senior officials and the attacks, but Sanders notes that some conclusions remain classified.
He said Saudi Arabia promotes an extreme and "very destructive" version of Islam.
Hillary Clinton has also come out in support of the bill. “Obviously, we’ve got to make anyone who participates in or supports terrorism pay a price, and we also have to be aware of any consequences that might affect Americans, either military or civilian or our nation,” she told ABC’s “This Week.”
Fifteen of the 19 hijackers in the September 2001 attacks, which destroyed the World Trade Center and killed thousands, were citizens of Saudi Arabia.
The stakes in New York for both Mr Sanders and Ms Clinton are higher than ever. After taking eight of the last nine nominating contests, Mr Sanders arguably has the better wind behind him.
Were he to win New York and take the largest share of its trove of 247 delegates, the effect would be electrifying. Which is precisely why Ms Clinton cannot let that happen.
The state should be Ms Clinton’s to lose. Unlike Mr Sanders who cut his electoral teeth in the relatively genteel climes of Vermont, she has lots of experience of New York’s especially rough brand of politics. She won the New York primary competing with Barack Obama for the nomination in 2008 and was sent by the state to the US Senate not once but twice.
