As with any trade deal, the Trans-Pacific Partnership agreement has winners and losers, and how they sort out will become clearer in the weeks ahead as details of the complex agreement emerge.

Unfortunately, many are making a rush to judgment on the agreement without giving it a fair hearing. Add in the heat generated by the nascent presidential campaign — with protectionist sentiment having re-emerged on both the right and the left — and you have the potential that Congress will kill the deal based on politics, not sound policy.

In June, President Obama had to collaborate with Republicans to keep his goal of signing a Pacific trade deal alive, a situation that exposed the leftward shift of the Democratic Party on issues of economic policy. The party of President Bill Clinton, which in the 1990s ushered in a new era of free trade, has retreated to the outdated concept of protecting jobs by shying away from global competition.

Since then, however, Donald Trump has arisen as the surprise frontrunner in Republican presidential primary polls, potentially changing the politics on that side of the aisle. Mr. Trump is an unapologetic protectionist. No sooner had 12 nations announced Monday they had reached an agreement, than Mr. Trump tweeted “TPP is a terrible deal.” Republicans who had supported the deal may have second thoughts about getting on the wrong side of an issue on which they see Mr. Trump scoring political points.

Meanwhile, the hard-left Democratic presidential candidate, Vermont Sen. Bernie Sanders, dismissed it as “disastrous.”

“Wall Street and other big corporations have won again. It is time for the rest of us to stop letting multinational corporations rig the system to pad their profits at our expense,” he said.

Sen. Sanders has raised legitimate concerns about a shrinking middle class and the concentration of wealth among a small group of the very rich, but seems to lose sight of the reality that successful corporations create jobs.

Of course, corporations can also ship those added jobs overseas, and some of that will happen if Congress approves the deal. As noted by the Wall Street Journal, it will help “U.S. giants like Nike Inc. ship goods home from overseas factories.”

However, on the other side of that coin are provisions that will allow U.S. manufacturers and computer software companies to fairly compete in the Pacific market, the fastest growing on the planet. The United States should not fear fair competition with anyone, and that is what U.S. negotiators of the TPP agreement set out to establish.

The signatories are the United States, Japan, Vietnam, Australia, New Zealand, Canada, Singapore, Chile, Brunei, Mexico, Malaysia and Peru. The deal would phase out thousands of import tariffs and regulatory impediments to international trade. It would demand universal access to the Internet among participating nations, uniform environmental standards, greater labor protections, and improved protection of intellectual property.

Tariffs that have inhibited U.S. exports of autos, agricultural products, advanced manufacturing machinery, information technology and other goods to the Pacific market will be lifted by the participating nations.

Legitimate concerns include the potential for currency manipulation to distort markets and whether the deal would give corporations too much power to block domestic policies that they contend interfere with trade.

It will now be up to members of Congress to evaluate the pros and cons. In making that evaluation, however, they should not lose sight of how difficult it was for the Obama administration to get so many countries to agree. In no such deal do all participants get everything they want, including the United States. Saying “no” will inhibit the nation’s ability to compete in a market that accounts for two-fifths of the global economy.

The coming vote will determine whether President Obama is able to achieve his “pivot to Asia” strategy. If the answer is no, there should be good reasons, not a rationale based on the politics of the moment.