Last week, President Donald Trump announced his plans to put stiff tariffs on all steel and aluminum imports.

Both candidates in the tight House special election in Pennsylvania have supported some form of tariff on steel and aluminum.

Democrat Conor Lamb, a former U.S. attorney and US Marine Corps veteran running to represent Pennsylvania's 18th congressional district, before a speech to an audience at the American Legion Post 902 on January 13, 2018 in Houston, Pennsylvania. Getty Images

Few policies championed by President Donald Trump have caused more blurring of political party lines than proposed tariffs on steel and aluminum imports. The president's trade goals have ruptured partisan divisions southwest of Pittsburgh, where Republicans and Democrats are fighting for blue-collar votes in a tight House special election. In the race for Pennsylvania's 18th District seat in Trump country, Republican candidate Rick Saccone and Democrat Conor Lamb have both signaled support for some form of tariff on metals. The contenders in next Tuesday's election aim to not alienate key constituencies in the district, like workers in the steel and aluminum industries or unions representing the region's laborers.

The reaction to the tariffs in parts of the district shows working-class areas may again react well to anti-trade rhetoric as Republicans and Democrats battle for control of Congress this year. Trump hopes his proposed tariffs can give Saccone an edge with blue-collar voters as the GOP tries to avoid losing in an area the president carried by 20 points in 2016, partly thanks to his pledges to crack down on unfair trade practices and protect American workers. But as Democrat Lamb has warmed to at least modest protectionist measures, it may not be a deciding factor for voters in the region. Political observers consider the election a key indicator of whether Democrats can win House seats in red pockets of the country and gain a majority in the chamber in November.

President Donald Trump speaks during a tour of the H&K Equipment Company in Coraopolis, Pennsylvania on January 18, 2018. Mandel Ngan | AFP | Getty Images

Trump's proposal has brought together strange bedfellows in Pennsylvania's 18th District. The traditionally Republican area has a wealthier and more educated populace than the median congressional district and a strong steel and energy industry presence. Saccone, a 60-year-old GOP state representative, "supports free trade as long as it's fair," his campaign said in a statement. If tariffs are required "to protect steel and aluminum jobs in Southwestern Pennsylvania, Rick would support those measures," the campaign added. At a recent debate, the Democrat Lamb said "we have to take some action to level the playing field," calling trade measures "long overdue." The 33-year-old former prosecutor added that he backs tariffs that "focus on China more so than our friends" like Canada. Former Vice President Joe Biden, who served in the Obama White House that defended the North American Free Trade Agreement and pushed for the Trans-Pacific Partnership, mentioned the need for "tougher" or "fairer" trade laws while campaigning for Lamb with union members outside of Pittsburgh on Tuesday. He did not specify what it would take to make trade laws more fair.

Key supporters back the tariffs

Two polls of the race released this week showed a statistical dead heat between Saccone and Lamb. A Gravis poll released Wednesday found Saccone held a 3-percentage point advantage, while an Emerson poll out Monday showed Lamb with a 3-percentage point edge. Both of those leads fell within the surveys' margins of error. Prevailing in the close contest means mobilizing key constituencies for both Saccone and Lamb. Saccone rallied with members of the district's energy industry this week, while Lamb spent part of his day Tuesday with union members.

David Podurgiel, a Rick Saccone supporter Jacob Pramuk | CNBC

Supporters of both Saccone and Lamb within those groups who spoke to CNBC largely showed support for steel and aluminum tariffs. "I love it," said David Podurgiel, a 52-year-old Canonsburg, Pennsylvania, resident and vessel operations manager for coal company Murray Energy's shipping operation. At a Saccone event Monday at a VFW post in the town of Waynesburg, Podurgiel told CNBC that he feels the tariffs fit with the "America First" polices Trump pledged as a candidate. He noted that Murray's shipping business counts U.S. Steel, a major steel producer based in Pittsburgh, as a customer. Jim McCaffrey, a senior vice president for coal sales at Consol Energy who backs Saccone, also told CNBC he thinks the tariffs could "revive the American steel industry." Some similar views on the tariffs emerged at Lamb's event with union members, who hardly support the president's overall platform.

Conor Lamb Jacob Pramuk | CNBC