Human trafficking — slavery, really — is a global scourge that requires a worldwide response. And yet, as with so many intensifying global challenges, the U.S. must lead.

The staggering scope of human trafficking, which may ensnare up to 20 million people worldwide, is most commonly associated with the adults and children trafficked for sex. But it includes children conscripted as soldiers and terrorists, as well as those sold into forced labor as depicted in the chilling recent New York Times series "The Outlaw Ocean."

One key tool in the fight against trafficking is the U.S. State Department's annual Trafficking in Persons (TIP) report, which was released last week. The report ranks 188 nations in four tiers based more on a government's response to trafficking than the problem's extent in that country. No nation, including ours, is perfect, but those in full compliance with the Trafficking Victims Protection Act are ranked in Tier 1.

Tier 3, conversely, consists of countries that do not comply and are not making sufficient efforts to do so. Malaysia was on that list last year. But this year it was elevated to "Tier 2 Watchlist," which has led some to claim that the upgrade was due to the Obama administration's push to include Malaysia in the Trans-Pacific Partnership, a 12-nation free-trade agreement that is still being negotiated.

That concern spurred 19 senators, including Minnesota Democrats Amy Klobuchar and Al Franken, to write a letter to Secretary of State John Kerry stating their "grave concern" that "a premature upgrade of Malaysia would undermine the integrity of the TIP process and compromise our international efforts to fight human trafficking."

The integrity of the process is indeed important and should not be politicized. "Usually, the report tends to be a very useful tool to actually get governments to move concretely and make reforms, whether it's legislation or processes or making commitments that they have said they are going to do but have not actually implemented," Sarah Margon, Washington director for Human Rights Watch, told an editorial writer. But, she added, "Our feeling is that Malaysia has not taken the necessary reforms that would merit an upgrade."

Because of the time frame, the TIP report did not account for the more recent discovery in Malaysia of mass graves, some likely containing persecuted Rohingya Muslims who were trafficked out of Myanmar, Sarah Sewall, a U.S. State Department official, said at a news conference. The country has made strides in compliance with TIP, Sewall said, but concerns remain.

The 19 senators should be joined by the rest of Congress in pressing the Obama administration for answers on Malaysia's status. And the administration, starting with Kerry's trip to the country this week, should insist that the government deliver the progress the report suggests. The Trans-Pacific Partnership deal may be in America's economic and security interests, but a trade pact should not be swapped for human rights concerns.

Still, it is important to keep the TIP report, and the U.S. leadership it represents, in context. "Is the report perfect? No. Some of this can be questioned," Klobuchar told an editorial writer. "But the fact that it exists and countries aspire to move up the list really makes it all worth doing, despite questions that can be raised about individual decisions."

Given the huge stakes in ruined lives, the ongoing U.S. fight against modern-day slavery should be unyielding.