WASHINGTON — Hillary Clinton, in an interview that aired Monday on NPR, said she “would not” rule out questioning the legitimacy of the 2016 election if Russian interference is deeper than currently known.

The comment, a remarkable step for the former Democratic nominee, exemplifies Clinton’s belief that President Donald Trump and his campaign could have knowingly received help from Russian operatives in the 2016 election.

Clinton has said previously that she conceded to Trump quickly and attended his inauguration because the nation’s peaceful transfer of power is critical. But her comments to NPR signal that as the depths of Russia’s interference are revealed she could envision a time when she questions Trump’s legitimacy as president.

NPR’s Terry Gross asked Clinton directly during the interview whether she would “completely rule out questioning the legitimacy of this election if we learn that the Russian interference in the election is even deeper than we know now?”

“No. I would not,” Clinton said.

Gross asked: “You’re not going to rule it out?”

“No,” Clinton said. “I wouldn’t rule it out.”

Clinton is in the midst of a media blitz to promote her new memoir, “What Happened,” a reflection on her stunning loss in the 2016 election and diagnostic for the Democratic Party going forward. The subsequent book tour has thrust Clinton back into the public eye after months largely out of the news.

In the book, Clinton casts Trump as a toxic but hapless leader who won the White House by preying on the nation’s fears. Nowhere in the book, however, does she directly question his legitimacy, although she certainly comes close in the 500-page memoir.

Clinton devotes an entire chapter to Russia, saying that the nation’s intervention in the 2016 election — which is currently being investigating by a host of congressional panels and a special counsel — led to Trump’s win.

“In many ways, Trump is the embodiment of everything they had been working toward, and the perfect Trojan Horse for Putin,” Clinton writes.

She adds, “No foreign power in modern history has attacked us with so few consequences, and that puts us all at risk.”

Clinton, in her interview with Gross, adds that there are likely no avenues, however, for her to challenge the 2016 results if she feels she needs to.

“Basically I don’t believe there are. There are scholars, academics, who have arguments that it would be, but I don’t think they’re on strong ground,” she told Gross. “But people are making those arguments. I just don’t think we have a mechanism.”

Clinton also mentioned that the Kenyan Supreme Court overturned their recent presidential election and ordered a new vote.

“What happened in Kenya, which I’m only beginning to delve into, is that the Supreme Court there said there are so many really unanswered and problematic questions, we’re going to throw the election out and redo it,” Clinton said. “We have no such provision in our country. And usually we don’t need it.”

Clinton’s comments are sure to further Trump’s deeply held belief that investigations into Russia — and Democrats’ calls for further pressure on the White House — are nothing more than the left’s attempts to rewrite the 2016 election and make up for Clinton’s loss.

“This whole narrative is a way of saving face for Democrats losing an election that everyone thought they were supposed to win,” Trump posted on social media in March. “The Democrats are overplaying their hand. They lost the election, and now they have lost their grip on reality.”

In her book, Clinton also wrote that once the election was over, she felt she needed to help the transition to Trump’s presidency go smoothly.

“Still, I felt a responsibility to be there,” she wrote about attending Trump’s inauguration, no matter how painful. “The peaceful transfer of power is one of our country’s most important traditions.”

And she made the same case hours after her crushing loss, as she stood before the nation and her supporters to publicly concede the election.

“Donald Trump is going to be our president. We owe him an open mind and the chance to lead. Our constitutional democracy enshrines the peaceful transfer of power,” she said. “We don’t just respect that. We cherish it.”

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