Hillary Clinton just broke with Obama on a major cornerstone of his legacy

Former Secretary of State Hillary Clinton on Wednesday said "as of today" she opposes the major trade deal known as the Trans-Pacific Partnership, a major break with an administration that considers the deal a cornerstone of President Barack Obama's foreign-policy legacy.

"As of today, I am not in favor of what I have learned about it," the Democratic presidential front-runner told PBS' Judy Woodruff in an interview during a campaign swing in Iowa. "I don't believe it's going to meet the high bar I have set."

The trade deal is the largest regional agreement in history, but it has come under fire from reliable Democratic constituencies - especially labor unions.

Clinton's top rival in the Democratic primary, Sen. Bernie Sanders (I-Vermont), has vehemently opposed the trade agreement. In an email to supporters earlier this week, Sanders said he would do "all that I can" to derail the deal he painted as good for Wall Street and large corporations.

Her opposition, however, puts Clinton in an awkward position, considering her history in the Obama administration.

As secretary of state, she praised and pushed the agreement numerous times. In past statements, she has touted the "economic opportunities" of the deal and claimed it would "lower trade barriers, raise labor and environmental standards, and drive growth across the region."

Earlier this year as she ramped up a potential campaign for president, however, Clinton began to shift from previous full-throated support, hedging her support or opposition on the results of a final agreement. Clinton's wavering stance reportedly irritated some White House aides during that process.

The Obama administration intensely lobbied skeptical Democratic lawmakers earlier this year to back a provision that would smooth implementation of the deal, which was finalized on Monday. Ultimately, that authority passed with mostly Republican support. 

Sometime over the next few months, both chambers of Congress will hold an up-or-down vote on the final agreement. The debate over the deal will likely become contentious in the heat of a presidential primary battle.

Clinton's opposition also draws a potentially notable contrast with Vice President Joe Biden, who is weighing a challenge to the Democratic front-runner. A spokeswoman for Biden told The Wall Street Journal on Wednesday that he "supports the TPP agreement and will help pass it on the Hill."

It's the second time in the past two weeks that Clinton has broken with the administration on a hot-button issue. Last week, she said she favored repealing the so-called "Cadillac tax" in the Affordable Care Act.

The White House didn't immediately respond to a request for comment.

Watch Clinton explain her opposition below: