(REUTERS/Chris Keane)

With Senate Democrats divided over whether to approve the Keystone XL oil pipeline in a vote Tuesday night, they won't be getting any guidance from the person poised to become their standard-bearer.

Hillary Rodham Clinton has no stated opinion on the matter.

A former secretary of state and U.S. senator and likely 2016 presidential candidate, Clinton has refused over the past several years to weigh in on the contentious debate. She has said that her connection to the State Department, which has been central to the Obama administration's review of the pipeline, prevents her from taking sides.

For Clinton, there is no upside to taking a stance. If she came out in favor of the pipeline, she would anger environmental and climate activists, including super PAC founder Tom Steyer and many other major Democratic donors. If she opposed it, she would be at odds with the business community.

Yet as she moves toward a presidential candidacy, Republicans have been trying to draw her into messy congressional debates. With embattled Sen. Mary Landrieu (D-La.) scrambling to round up votes from her Democratic colleagues ahead of Tuesday night's scheduled Senate vote, Republicans are criticizing Clinton for remaining neutral on such a high-profile and contentious issue.

“She wrote a book called 'Hard Choices,' but she wouldn't take an opinion on the Keystone Pipeline," said Tim Miller, executive director of America Rising, a GOP group leading the attack on Clinton. "She may be the only person in America without a position on the Keystone Pipeline at this point.”

A Clinton spokesman did not immediately respond to a request for comment.

During multiple speaking appearances and interviews in Canada earlier this year, Clinton has been asked about the Keystone Pipeline. In June, she told The Globe and Mail:

"We have no better relationship. [But] this particular decision is a very difficult one because there are so many factors at play. I can’t really comment at great length because I had responsibility for it and it’s been passed on and it wouldn’t be appropriate, but I hope that Canadians appreciate that the United States government – the Obama administration – is trying to get it right. And getting it right doesn’t mean you will agree or disagree with the decision, but that it will be one based on the best available evidence and all of the complex local, state, federal, interlocking laws and concerns."

As she told an audience in March in Vancouver, "No comment."