WASHINGTON (Reuters) - President Donald Trump has alarmed the Republican establishment and world leaders by threatening tough steel tariffs, a message that might be meant not just to shake the world trade order but to help defend a congressional seat in Pennsylvania.

FILE PHOTO: U.S. President Donald Trump waves upon his arrival in West Palm Beach, Florida, U.S., March 2, 2018. REUTERS/Kevin Lamarque

Some Republican strategists said Trump’s tariff threat appeared to be timed, at least in part, to sway voters in the steel country of Pennsylvania, including its 18th District where Republican Rick Saccone and Democrat Conor Lamb are facing off.

In a special election on March 13, the two will vie to replace Republican Tim Murphy, who resigned in October in a sex scandal. If Saccone loses, it would be a blow to Trump, the first loss by Republicans of a seat in the House of Representatives since he took office in January 2017. The results will not affect Republican control of the chamber.

Trump has endorsed Saccone and is scheduled to visit the Pittsburgh area on Saturday for a campaign event. Saccone met Trump on arrival for a similar event in January.

Republican strategist Ford O’Connell said Trump’s stance on steel and aluminum tariffs could help Republicans, not only in southwestern Pennsylvania, but across the industrial Midwest.

“The timing definitely helps Saccone,” O’Connell said.

The 18th District covers steel, farm and coal country on the West Virginia border, as well as well-to-do Pittsburgh suburbs. Trump won the district by nearly 20 points in the November 2016 presidential election, helping him carry the pivotal battleground state.

But in recent political races in other states, Democrats, upset by Trump policies, have been energized to turn out to vote. In the Pennsylvania race, Lamb is rising in the polls and is neck and neck with Saccone, who has said: “I was Trump before Trump was Trump.”

Peter Navarro, the White House trade and manufacturing policy director, defended Trump’s trade plan on Fox Business Network’s “Varney & Co.” show on Monday. “Of course, if you go to Ohio or Pennsylvania, or you go to the heartland of American Main Street, there’s universal support,” he said.

Trump threatened to impose 25 percent steel and 10 percent aluminum tariffs in an announcement on Thursday, prompting a steep stock sell-off and expressions of concern about a possible trade war from Washington to foreign capitals.

‘THIS IS A WINNER’

Establishment Republicans should not be surprised that Trump is following through on his tough-on-trade campaign pledge, said Chris Barron, a pro-Trump Republican strategist.

“If Republicans are going to hold on to the majority in the House, they need to hold on in places like Pennsylvania. This is a winner,” he said, adding the rally on Saturday would be good for Trump, who will get positive feedback from the crowd.

“It’s going to be hard to talk the president back from that, because he’s going to feel first-hand that support from those grassroots working-class voters,” Barron said.

Democrats said the tariff issue would likely be a factor in the 18th District race, but one that would cut two ways.

Pennsylvania Democratic strategist Mike Mikus said: “The issue of steel tariffs is a very popular idea here in western Pennsylvania. However, I don’t believe it will be enough to help Rick Saccone in this election. I don’t view it as a game-changer because the issue has been championed by Democrats for so long.”

Republican strategist Mike DeVanney said tariff rhetoric may help Saccone, but that any boost could be muted in the diverse district.

He added that the president’s comments could backfire. “It’s not without risks in equally energizing Lamb’s base,” DeVanney said. “President Trump is obviously a figure who can energize and divide, depending on who’s listening.”