The politics of tariffs are complicated. A Democrat just introduced a bill to make Trump's proposals law.

LINCOLNVILLE, Maine — Former President Donald Trump calls himself a “tariff man” and says the taxes on imported goods “are the greatest thing ever invented,” so it’s no surprise Vice President Kamala Harris has attacked the centerpiece of the GOP nominee's economic agenda as bad policy.

What’s more surprising, however, is that one House Democrat just introduced a bill to codify Trump’s 10% across-the-board tariffs, revealing how the long-dormant trade policy splits both parties.

Tariffs can trace their roots to ancient Athens and other historical civilizations and were the main source of revenue for the federal government until 1914, when the income tax supplanted them. But they largely fell out of favor during the late 20th century as the U.S. led a global free trade revolution.

Knocking down trade barriers slashed the cost of consumer goods and grew many economies around the world. But critics say unfettered free trade also decimated American manufacturing and the well-paid, often unionized, jobs that came with it since domestic factories were unable to compete with the lower costs of making things abroad.

“Other countries are going to finally, after 75 years, pay us back for all that we’ve done for the world, and the tariff will be substantial,” Trump said said this week.

Rep. Jared Golden, a heterodox moderate Democrat from Maine who is facing a tough re-election this year, introduced the bill Wednesday with the aim of promoting domestic manufacturing and limiting U.S. reliance on foreign goods.

“While it is undoubtedly true that Pres. Trump is the first in my lifetime to lead on tariffs, he’s hardly the first one to think about it,” said Golden in an interview. “Our Founding Fathers understood in the earliest years of the nation that we should avoid becoming a nation of consumers of foreign goods because it creates dependency.”

Harris and her campaign have slammed Trump's idea for across-the-board tariffs, saying they would raise prices on consumers who are already struggling with record-high costs due to inflation.

“It would be a sales tax on the American people,” she said in an interview with MSNBC on Wednesday. “You don’t just throw around the idea of just tariffs across the board, and that’s part of the problem with Donald Trump... He’s just not very serious about how he thinks about some of these issues.”

Trump’s tariff plan has critics on his side of the aisle as well.

Libertarian-leaning Sen. Rand Paul, R-Ky., introduced a bill this month to prohibit any president from raising tariffs without getting sign off from Congress first — a clear shot at Trump who has said he would enact his tariff policy through executive action alone. (Trump was able to raise tariffs during his first term without congressional approval.)

Despite Harris and other attacks on Trump's tariffs, the Biden-Harris administration decided to keep some of the tariffs Trump imposed during his first term on Chinese steel and aluminum and even increase the fees on strategic sectors like electric vehicles and semiconductors.

Harris did not address those tariffs when asked about them in the MSNBC interview.

Still, Biden and Harris have consistently criticized across-the-board tariffs as “indiscriminate” instruments that risk “undermining our alliances,” arguing targeted sanctions do not carry the inflationary risks of wider spread one.

Golden, like some others who favor tariffs, says an across-the-board tariff would be good for American workers and national security regardless of whether Trump supports the idea or not.

While Trump does not, Golden acknowledges that tariffs would push up prices on imported goods, but says those higher costs would make domestically produced products more competitive and put upward pressure on quality since imported products could no longer compete on price alone.

“It made sense after World War II to pursue globalization because we were one of the last industrialized economies left standing,” Golden said. “That model no longer applies today.”

Economists are generally far more negative about tariffs. Most say the data is clear that freer trade leads to greater economic growth and they say Trump's across-the-board tariffs would raise inflation and could cost jobs.

Politically, however, tariffs appear fairly popular, with a recent Reuters/Ipsos poll finding 56% of Americans support the idea, and that number is likely to go be even higher in a Trump-leaning district like Golden's, which, like many others, saw a raft of plant closings over the past 40 years.

This article was originally published on NBCNews.com