Sen. Rob Portman (R-Ohio) is one of several vulnerable first-term Republicans who are pushing global trade pacts. (Al Behrman/Associated Press)

From the largely shuttered steel mills around Scranton in Pennsylvania, to the devastated manufacturing region around Kansas City , Missouri, Senate Republicans face the daunting task of promoting global trade while defending seats in states that have seen so many factories fade into history.

For the new GOP majority in the Senate, the highest economic priority in 2015 is to push through legislation known as ‘Trade promotion Authority,’ or ‘fast-track authority’ that would allow the president greater negotiating flexibility on trade deals. Then they hope to approve a sprawling Pacific-rim trade pact that would include countries representing 40 percent of the global economy.

It’s a process that won support last week in the Senate Finance Committee from such vulnerable first-term Republicans as Sens. Rob Portman of Ohio and Patrick Toomey of Pennsylvania.

Three other Republicans are running in their first reelection from the Midwest, each publicly supporting the idea of the trade deal because of the purported benefit of boosting U.S. export sales. The full Senate is slated to take up Trade Promotion Authority (TPA), the specialized process for approving deals that President Obama is seeking, possibly early next week.

While Democrats nationally are split on the efficacy of these pacts, rust-belt Democrats are largely united in opposition and plan to use the issue against the GOP incumbents. They aren’t afraid to criticize Obama’s proposals or the Clinton administration’s 1990s trade record, saying that it was past free trade deals that sped along the decline of the U.S. manufacturing base.

“We have learned from our past mistakes that we need protections built into these trade deals that do not allow American companies, American workers, to be placed at a disadvantage,” said former Ohio governor Ted Strickland (D), who is challenging Portman.

Many Democrats in the region see an anti-trade message as a way to appeal to a key voting bloc — the white working class — that has increasingly abandoned the party over the last 15 years, because that group has also felt left behind by the global economy.

“They don’t want us to rush into another trade deal,” Strickland said.

Midwest Republicans are keenly aware that their region has been hit hard by disappearing factory jobs, placing these GOP senators in a tough spot heading into the 2016 elections as they tout a message that might not resonate.

“I’m for free and fair trade. I certainly recognize that it’s not the most politically popular thing to be for,” said Sen. Ron Johnson (R-Wis.), who faces a possible rematch with former senator Russ Feingold (D-Wis.)

From 2005 to 2010, Wisconsin lost more than 75,000 manufacturing jobs — almost 16 percent of all such workers — before a modest resurgence during the last four years brought that sector back to its 2008 workforce level. “It’s very easy to show those anecdotal pieces of information or examples where people are really harmed,” Johnson said.

Johnson and other Republicans are trying to sell voters on the idea that exports create higher-paying work, and that the United States has to lead the global economy — or China will dominate.

Portman cited his position of being “strong on enforcement, strong on stopping the currency ma­nipu­la­tion, strong on ensuring we have a level playing field.” He helped win approval for a measure to be included in the legislation that would ensure greater scrutiny of China’s efforts to manipulate its currency to sell cheaper products.

“But we don’t want to shoot ourselves in the foot and not expand exports, because those are great-paying jobs in Ohio. Our workers, our farmers rely on them,” Portman said.

Democrats are betting that so nuanced an argument will fall flat across the Midwest. In the 2010 campaign, Senate Republicans picked up a net of six seats, four of which came from rust-belt seats previously held by Democrats in Pennsylvania, Indiana, Illinois and Wisconsin. In addition, open seats in Missouri and Ohio that once figured to be competitive turned into routs for Sen. Roy Blunt (R) and Portman.

Republicans successfully tapped into middle-class anger, particularly that of white voters who thought that the early years of the Obama administration were spent on issues that did not connect with their economic needs.

That trend held in the 2014 elections, another debacle for Democrats. White Catholics — a predominant voting bloc in the Midwest — supported Republicans by a margin of 60 percent to 38 percent, according to exit poll data.

[ Read about Democrats questioning the timing of passing the 2010 health law. ]

Now, with all six of those Midwestern seats up in 2016, Democratic strategists privately say that their meager agenda of the past few years in appealing to those white voters could be turned around by using GOP support for trade deals. Many of those voters think Washington, by pushing a series of global trade over many decades, sold them out for corporate benefactors whose bottom lines grew by securing cheaper workers in foreign countries.

Take Pennsylvania and Ohio: Toomey, the former head of the pro-trade Club for Growth, and Portman, a trade representative for the Bush administration in 2005 and 2006, present resume items that anti-trade Democrats will try to exploit.

In the last decade, Pennsylvania has lost 120,000 manufacturing jobs, more than 17 percent of that workforce, and there’s been no bounce-back during the recent recovery, according to the Bureau of Labor Statistics. The losses are more devastating over the 20-year arc, a time frame that coincides with the passage of the North American Free Trade Agreement during the Clinton administration.

In 1995, Pennsylvania had almost 900,000 manufacturing jobs, more than 300,000 of which have since disappeared. Ohio had more than 1 million manufacturing jobs 20 years ago, and now, despite a slow and steady recovery in the last five years, the state has about 680,000 workers in manufacturing.

It has left some centrist Democrats sounding more like radicalized local union organizers.

“It seems like every time we have a trade deal, we get the short end of the stick. I have to believe that, in a lot of states in the Northeast and the Midwest, that they’ve experienced the same thing,” said Sen. Robert P. Casey Jr. (D-Pa.), an Obama confidant who is one of the state’s most popular figures. “We’re always promised that, next time, the labor protections are going to be stronger; next time, the environment protections are going to be stronger; next time, we’re going to get that level playing field. And it never seems to arrive.”

Some Democrats are even using their opposition to TPA as a way to separate themselves from the president and link the Republicans to Obama. Jason Kander, the Missouri secretary of state, who is challenging Blunt in 2016, repeatedly criticized the “President Obama and Senator Blunt” trade agenda in a recent interview.

On Thursday, the Federal Reserve Board of Kansas City declared its region’s factories “had their worst month in quite some time, as exports continued to drop.”

Republicans believe that they can position themselves in a way that voters will see them as forward-leaning but also geared toward protecting local interests.

“Voters get it; they want more exports and they also want imports coming into this country to be fair,” Portman said.

And corporate America stands ready to defend those Midwest Republicans.

“We certainly worry about the elections, and we’re going to be very involved in those,” Thomas J. Donohue, president and CEO of the U.S. Chamber of Commerce, said last week after testifying in favor of the trade deals before the Finance Committee. “We’re going to be there in 2016.”