Hillary Clinton protects left flank with TPP opposition

Three words help explain why Hillary Clinton now opposes the Trans-Pacific Partnership trade accord – after once laying the groundwork for it as secretary, and before the public has even seen the details.

Presidential primary politics.

Her newfound opposition – after not taking a position on the issue for months – protects her left flank against Bernie Sanders’ challenge; it helps her solidify her support with organized labor; and it makes Vice President Joe Biden the only Democrat in favor of the accord (if he gets into the race).

So if Clinton is worried about Sanders’ poll position and the threat of Biden entering the 2016 race, this is a smart move.

RELATED: Hillary Clinton comes out against the Trans-Pacific Partnership

It’s also consistent with modern Democratic politics: In the 2008 Democratic primaries, both Barack Obama and Hillary Clinton railed against NAFTA and free trade accords. But after winning the Democratic nomination, Obama warmed up to free trade – and he’s now made this TPP trade accord a chief goal in his final months in the White House.

So it wouldn’t be surprising if Clinton makes a similar move back to the middle if she wins the nomination next year.

But what’s good primary politics comes at a cost – for both her and the Obama administration in which she served.

For starters, Clinton’s opposition comes across calculating and political instead of principled. Indeed, in her book “Hard Choices,” Clinton said of trade: “Despite all its problems, a more open trading system has lifted more people out of poverty in the last thirty-five years than at any comparable time in history.”

In 2012, as secretary of state, Clinton called TPP “the gold standard” in trade agreements. “This TPP sets the gold standard in trade agreements to open free, transparent, fair trade, the kind of environment that has the rule of law and a level playing field. And when negotiated, this agreement will cover 40 percent of the world’s total trade and build in strong protections for workers and the environment,” she said.

Her rivals have already pounced on her for being a Johnny Come Lately in opposition. “I didn’t have one opinion eight months ago and switch that opinion on the eve of debates,” Martin O’Malley said after the news of Clinton’s announcement.

And it serves as Clinton’s biggest break yet with President Obama and his administration.

After all, Clinton supported the Iran deal – a move that helped unite the Democratic Party around it.

But now, Obama and his team face a situation where the entire Democratic ‘16 field (for now) opposes the TPP accord, which won’t make it easier to twist Democratic arms to get congressional ratification.

The Obama White House will have to get much of its support from Republicans – just like it did in winning fast-track authority earlier this year. 

This article originally appeared on NBCNews.com.

Hillary Clinton and Trade

Hillary Clinton protects left flank with TPP opposition