Republicans in Congress, scrambling for cover from midterm headwinds that could sweep them from power, are struggling in a political environment dominated by the unpredictability of President Trump’s polarizing leadership.

As the first votes of the 2018 elections were cast Tuesday in Texas primaries, Trump blew up the Republicans’ carefully crafted strategy to run on tax reform’s economic expansion with unanticipated plans to levy steep tariffs on imported steel and aluminum.

Republicans warn a trade war could depress job and wage growth that has accelerated since passage of the tax overhaul, sapping their hope for political recovery by November. But Trump is unconcerned, ignoring pleas to reconsider from Republicans on Capitol Hill.

“There is a theory that if a country doesn't have steel, it doesn't have a country,” Trump said Tuesday during a news conference. “So this is more than just pure economics.”

In the heartland, where Trump built his unlikely 2016 victory, this message resonates. The president lured historically working-class Democrats into the Republican fold by promising to crack down on other nations’ unfair trade practices and revive languishing manufacturing hubs.

But this year, in the battleground suburban House districts likely to decide the fate of the Republicans’ 24-seat majority, it could backfire. The educated professionals who predominate these upscale enclaves are fiscally conservative — and dissatisfied with Trump.

Populist economics is tough sell with this cohort. It could complicate the Republicans’ effort to sustain the improving-but-precarious image of the Tax Cuts and Jobs Act, which party strategists consider crucial to holding this voting bloc and holding their majorities.

That depends largely on voters maintaining views of the national economy — and their personal pocketbooks — that are as favorable and optimistic about the future as they have been in years. Republicans fear the fallout from tariffs would render that impossible.

“There’s a high level of concern about interfering with, what appears to be, an economy that’s taking off in every respect,” Senate Majority Leader Mitch McConnell, R-Ky., said during a news conference. “We are urging caution that this develop into something much more dramatic that could send the economy in the wrong direction.”

In a Quinnipiac University poll conducted Saturday through Monday, voters opposed tariffs on steel and aluminum by a wide margin, 50 percent to 31 percent. The disparity was even greater, 64 percent to 28 percent, when they were asked if they agreed with Trump that a trade war would be good for the U.S. and easily won.

Democrats have their own challenges to overcome, despite the historical advantages of running in a midterm in which their party does not control the White House and is benefiting from Trump’s low job approval and personal favorability ratings.

Republicans hold a slim 51-49 majority in the Senate, but Democrats are defending 10 seats in states Trump won, threatening the GOP in only two — Arizona and Nevada. If the election were held today, Republicans would probably pick up Senate seats, even as they possibly lose control of the House.

Grassroots liberals’ demand for new gun control regulations, in the aftermath of the shooting massacre at a high school in Parkland, Fla., that left 17 dead, could squeeze Democratic Senate incumbents running for re-election in red states that Trump won overwhelmingly. Democrats dismiss the concern.

Another potential hurdle: Voters are increasingly bullish on the $1.4 trillion tax package, which Democrats unanimously voted against in December. Democrats claim voters are beginning to have second thoughts about the Tax Cuts and Jobs Act.

“They had a very good January, but America is now learning what’s in this bill and turning against it,” Senate Minority Leader Chuck Schumer, D-N.Y., said. “The idea that it’s going to be a panacea to save the Republicans? I don’t think it’s true at all.”

The Democrats biggest confidence-builder, by far, is the enthusiasm gap. Liberals, energized by opposition to Trump, are more excited to vote this fall than their conservative counterparts.

For Democrats who have been involved in national politics over the past 10-15 years, this year’s midterm reminds them 2006 and 2008, two consecutive wave elections that propelled their party to huge House and Senate majorities.

“If you put out a shingle and say: ‘Democratic meeting tonight,’ you’ll fill the room,” Rep. Gerry Connolly, D-Va., said.

And for Democrats that experienced the lean years in 2010 and 2014, when Republicans won control of the House and then the Senate in major swings of their own — they roll their eyes when they hear the GOP insisting that Trump won’t be the major factor that works against them this year.

It’s just what they tried to convince themselves about former President Barack Obama.

“That’s ‘whistling past the graveyard’ thinking. And, I understand it; we engaged in it ourselves,” Connolly said.