Democratic presidential candidate Hillary Rodham Clinton speaks to supporters during a rally June 14 in Des Moines. (Charlie Neibergall/AP)

The Sunday dust-up over trade between Hillary Rodham Clinton and Sen. Bernie Sanders (I-Vt.) was a clash waiting to happen — and a revealing look at how the two candidates for the Democratic presidential nomination are likely to be circling one another in the coming months.

Where Sanders stands on the Trans-Pacific Partnership (TPP) agreement has long been clear. He is plainly and simply against it. Clinton’s current position is ambiguous. She is skeptical but wants to see a completed agreement before she’ll decided whether it’s good or bad.

Where Sanders stands on giving the president fast-track authority also has been clear. He opposes it, as he opposes the trade deal itself. Where Clinton stands on that is no more clear after her Sunday comments.

She had more to say on Sunday than she’s said before. She has allied herself with Democrats who currently oppose the treaty without committing herself to opposing the treaty. Ultimately, she could end up standing with President Obama, who has been abandoned by his own party on this, or with those who want to sink the deal.

Clinton had remained silent on trade as long as she could, probably longer. By claiming, correctly, that there was not a deal to support or oppose, she was looking for the maximum space to let the politics of the issue ripen or perhaps for the divisions within her party to lessen in some way.

When the fast-track legislation began to make its way through Congress, she was unwilling to say where she stood. Her advisers repeatedly said that fast-track was merely a process issue, not a substantive one, something for Congress to deal with but not one that she needed to weigh in on. The big issue, they said, was the trade agreement itself and that was still in negotiations.

Clinton had promoted an Asian trade deal as secretary of state — or at least the idea of it. She saw merit in trying to negotiate such a pact as part of the larger U.S. policy under Obama of paying more attention than previous administrations to the challenges of the rising power of China and the opportunities of deepening alliances with other Asian nations.

And backing free-trade agreements runs in the family. Former president Bill Clinton had successfully campaigned for and won approval of the North American Free Trade Agreement (NAFTA) despite strong opposition within his party.

As the political wars over the trade deal heated up, Clinton found what she thought a safe political haven in the space between concept and execution, between the meritorious idea of the 12-nation TPP and the specific details contained in a final agreement. Until those details were known — and it’s not clear when the administration will complete the negotiations — she felt comfortable reserving her options.

Two things intruded on that safe haven. One was the arrival of Sanders as an energized presidential candidate with a following on the left of the Democratic Party. He’s not the only one among Clinton’s opponents who wants to sink the trade deal. Former Maryland governor Martin O’Malley has the same position. But Sanders is getting the attention and drawing the crowds. His increasingly pointed criticism of Clinton has made her posture far less tenable.

Before he returned to Iowa for a weekend of campaigning, Sanders appeared at a breakfast hosted by the Christian Science Monitor. He was asked to offer criticisms of Clinton. He prefaced his answer by saying that, while he liked and respected Clinton, the two had serious disagreements that should be debated during the campaign.

“You know my view on the TPP,” he said. “Trade policies have been disastrous. Secretary Clinton, if she’s against this, we need her to speak out. Right now. Right now. And I don’t understand how any candidate, Democrat, Republican, is not speaking out on that issue.”

There was more, however, from Clinton’s positions on the Keystone XL pipeline and the USA Patriot Act to his attacks on what he calls “the billionaire class” and what her policies are to deal with them. “What is the secretary’s position?” he asked about each.

The other big change was the rebellion by House Democrats on Friday against the pact, a vote that has vastly complicated the administration’s hopes of winning approval for fast-track authority and puts the entire trade deal in jeopardy.

When Clinton showed up in Des Moines on Sunday, she was forced by events and circumstances to take up the issue. What she did was tie herself to House Minority Leader Nancy Pelosi (D-Calif.) and other Democrats in the House. She urged Obama to listen to the concerns of Pelosi and others and use them as leverage in the negotiations over the trade agreement. As before, she said if the ultimate agreement falls short of her measuring sticks, she would oppose it.

Clinton is in a unique position. If she were to come out against the TPP now, it’s likely that her opposition would scuttle it. Obama probably could not overcome the combined opposition from organized labor, many Democratic elected officials and his former secretary of state. But supporting it even in general terms provides a bigger opening for Sanders and others on the left.

Clinton isn’t prepared to do either, at least not yet. At some point, she will have to signal up or down. For now she is trying to bridge the divide in her party, and the strains are showing.