Can Hillary Clinton step out of Bill's NAFTA shadow?

As first lady, Clinton backed NAFTA and spoke highly of it at stops for the administration. But once she was elected to the Senate and later ran for president, her support of free trade -- and her husband's landmark agreement -- began to wane. On the campaign trail, Clinton acknowledged that NAFTA has "hurt a lot of American workers" and advocated for broad reform of trade policy. President Barack Obama's campaign even used the flip-flop against Clinton during the 2008 primary.

But after Clinton lost the nomination and agreed to serve as the President's Secretary of State, she began to warm up to free trade, and particularly the TPP.

In her memoir, which Clinton's spokesman said was her most updated statement on the TPP, Clinton wrote, "It's safe to say that the TPP won't be perfect. No deal negotiated among a dozen countries ever will be - but its higher standards, if implemented and enforced, should benefit American businesses and workers."

That history worries some labor leaders who are prepared to hold Clinton to a standard that includes her support of free trade agreements.

AFL-CIO President Richard Trumka told CNN the issue of free trade could hang over Hillary Clinton in 2016. Sen. Bernie Sanders of Vermont says he'll make it a centerpiece of his campaign if he runs for president.

And union workers across the country - including some who lined up to see Clinton speak at a labor hall in 2014 - are talking about it, too.

"I think NAFTA itself will be remembered for as long as this generation draws a warm breath," Richard Trumka said in an interview. "When I talk to people about it, they don't remember that it was a Republican majority that passed NAFTA. They remember that it was President Clinton."

Labor leaders see Clinton's 1994 signing of NAFTA, which created a free-trade zone with Canada and Mexico, as the moment when blue collar wages began to stagnate.

Trumka said that free trade -- especially the TPP -- is one of the biggest priorities for the AFL-CIO and something that the group will use to gauge their support of candidates in 2015 and 2016. The issue is part of the group's "Raising Wages" priority plan which looks to raise the wages of all Americans.

The longtime labor leader, whose relationship with the Clintons goes back decades, said it was up to Hillary Clinton whether the legacy of NAFTA will hurt her campaign.

"It all depends on what her position is on trade. If her position on trade is that NAFTA is really a good thing and I want to continue it, it will definitely hurt her," he said. "All politicians, Democrats and Republicans, take about raising wages. But you can't be for raising wages while being for the same old trade policies."

That's where the Trans-Pacific Partnership — which liberal activists have taken to calling "NAFTA on steroids" — comes in.

It isn't only Trumka, though, that will likely apply pressure on Clinton regarding free trade. Two outspoken liberal senators -- both of whom have been followed by 2016 speculation -- have come out strong against the TPP.

Sanders, an independent who caucuses with Democrats, came out against the TPP earlier in 2014 and recently wrote a letter that accused the White House of crafting the deal in secret.

In an interview, the outspoken senator that while the concept of trade "is a good idea," trade agreements like NAFTA and TPP have been raw deals for American workers.

"It was very clear to me that any agreement that forces American workers to compete against desperate, desperate people who are working for pennies an hour is grotesquely unfair," Sanders said, recalling the 1990s when he traveled to Mexico to see the working and living conditions of workers producing goods sold in the U.S.

Unlike some labor and liberal leaders, Sanders does not hang NAFTA on Hillary Clinton. "Hillary Clinton was not the president. Bill Clinton was the president," he said. "Hillary will have to speak to her own views on trade."

That said, though, Sanders has brought free trade up on every trip he has made to Iowa -- the first-in-the-nation caucus state -- and when asked whether he would make the issue a key part of his possible presidential run he bluntly said: "I will give you a three letter answer to that - the answer is y-e-s."

Joining Sanders is Sen. Elizabeth Warren, who told an AFL-CIO audience recently that liberals "believe in trade policies and tax codes that will strengthen our economy, that will raise our standard of living, that will create American jobs because we will never give up on these three words: made in America."

Warren has also written a letter to U.S. Trade Representative Mike Froman questioning the deal.

The fact that Warren and Sanders are involved means this issue is not going away, especially for Clinton. Both represent the former first lady's left flank and are politicians who don't even need to run for president to dictate some of the issues that become big campaign issues.

Bill Clinton still defends NAFTA as a good deal for America. Just last November, at the 10th anniversary of the Clinton Library, the former President said, "NAFTA is still controversial but people will thank me for it in 20 years."

Hillary Clinton has waffled on the issue, though.

As first lady, Clinton backed NAFTA.

"I think that everybody is in favor of free and fair trade," she said during a meeting with union workers in 1996, "and I think that NAFTA is proving its worth." In her 2003 memoir, "Living History," Clinton also writes glowingly about NAFTA, including it among her husband's "legislative victories" and noting it would "expand U.S. exports, create jobs and ensure that our economy was reaping the benefits, not the burdens, of globalization."

But when she entered the Senate in 2000 and ran for president in 2008, Clinton's tune on free trade began to change. She conducted a study as senator that found the agreement hurt New York workers' ability to sell goods in Canada and spoke out against NAFTA during her 2008 campaign.

"NAFTA and the way it's been implemented has hurt a lot of American workers," Clinton said at a 2007 forum with the AFL-CIO. "Clearly we have to have a broad reform in how we approach trade. NAFTA's a piece of it, but it's not the only piece of it."

Clinton lost her race for president, though, and went on to serve as Barack Obama's secretary of state. In the role, she oversaw the President's much noted pivot to Asia. At the center of that move was the TPP.

"One of our most important tools for engaging with Vietnam was a proposed new trade agreement called the Trans-Pacific Partnership (TPP), which would link markets throughout Asia and the Americas, lowering trade barriers while raising standards on labor, the environment, and intellectual property," Clinton wrote in her 2014 memoir "Hard Choices."

As secretary of state, Clinton also talked up the benefits of the TPP and during a trip to Korea in 2011, she advocated for "as few barriers to trade and investment as possible."

When asked for Clinton's current position on free trade and the TPP, a spokesman pointed CNN to what the former secretary of state wrote in her book.

Republicans have picked up on the problem for Clinton and have started to point out her changes in opinion. Before Clinton went to Michigan last year to endorse candidates, America Rising PAC, an anti-Clinton communication and research group, questioned Clinton's "phony populism on free trade."

"A peculiar thing happens every time Hillary Clinton decides to run for President," the group said in a blog post. "Her views on free trade start sliding left and she calls for a 'time out' on free trade agreements."

These Republican attacks - and more likely to come - show the political problem Clinton faces. If she runs for President, she will either have to woo labor and liberal leaders by blasting agreements like TPP and NAFTA and risk looking like she is backtracking on her State Department years. Or she can embrace deals that she made at State and risk what has become eager liberal anger.

For all the comparisons, though, the TPP would actually be a much different -- and more comprehensive -- trade deal than NAFTA was.

Older pacts have mostly dealt with moving goods into and out of countries. But in the 12-country Pacific Rim deal, U.S. negotiators are pushing for rules that would help companies -- especially pharmaceutical drug-makers -- extend their patents and copyrights for much longer periods, keeping generic medicines off poorer foreign countries' markets.

They're working to create a tribunal that would give corporations a venue to challenge whether governments' rules and regulations are in line with their obligations under the trade deal.

And they're crafting chapters on environmental protections, labor rights and the digital economy. They're trying to prevent countries from restricting where data servers can be located, or what data companies can move across international borders.

The Trans-Pacific Partnership, like NAFTA, includes Canada and Mexico. But the deal's real pearl is Japan -- a potentially huge market for U.S. food, natural gas and more. It's a wealthy economy that American businesses haven't been able to crack.

But Japan is bogged down by its own political challenges. The country's agricultural interests are especially influential in its legislature, and they've resisted opening their ports to American rice, beef, pork and wheat -- which, in turn, has infuriated U.S. farmers. For more than a year, it's been a huge sticking point that has delayed progress on the deal.

That's why the Trans-Pacific Partnership debate isn't going away.

Trade agreements take years to come together. Even after the presidents and prime ministers announce they've struck a deal, the wording must be scrubbed and translated into each country's language -- a process that takes months. Then legislatures, where anger about their lack of a role in the negotiations has often simmered for years, might insist on changes. Different countries' elections and changing political tides can complicate things even more.

The best-case scenario for Obama is that the Trans-Pacific Partnership could be approved by Congress at the very end of his presidency.

And that's if a deal can be struck soon -- which is unlikely. Negotiators already blew their goal of reaching an agreement in 2012. Then they missed their own deadline in 2013. And again in 2014.

Much more likely is that the next president will have decisions to make about whether and how to finalize the negotiations -- or, at least, whether to sign the deal.