By winning a majority in the House of Representatives, the Democrats have a great opportunity. They shouldn’t waste it.

They should use the opportunity to govern — to pass legislation that helps the country and helps beleaguered constituencies in particular.

This would sound stupidly obvious, except lately that isn’t how Democrats have defined themselves. In the era of Trump, they have largely defined themselves by what they are not.

Not Trump. Not bounded in their revulsion for him. Not ceasing to talk about investigations of him. Not believing that Americans who support him are not, like him, loathsome.

This plays well in the Democratic echo chamber. It will not win crossover voters where the party will need them, in Ohio and in Pennsylvania.

Tom Steyer, the retired hedge fund billionaire and Democratic activist, says the Democrats should immediately initiate impeachment proceedings. He says they won by campaigning to hold you-know-who accountable.

But they didn’t. They won on health care.

They should pass a bill to back up what they have been saying about health care and protecting preexisting conditions. They should legislate support for access to broadband in rural areas and in schools that serve mostly underprivileged students.

They should pass an infrastructure bill and a bill to finally start the country on high-speed rail.

Gail Collins, in the New York Times, snarkily refers to such bread-and-butter spending as pothole repair. Here’s the deal: In the Rust Belt, potholes matter.

Don’t worry that the Republican-controlled Senate won’t go along or that the little jefe in the White House won’t go along. If they do, the country wins. If they don’t, the choice in 2020 is that much clearer.

If you want to hold hearings, hold a hearing about something that affects Americans in the communities that voted for Trump, like the opioid crisis. Haul in local police chiefs and pharmaceutical CEOs and, most importantly, drug users and recovering users.

Ask addicts why they became addicts and listen to their answers. Then start on solutions. It won’t be easy, but if people see you are listening, maybe not so many will feel compelled to cast a protest vote, as they did in 2016.

It won’t help in the Trump Belt for the House majority to reiterate its belief in its moral superiority. It won’t impress crossover voters and may actually alienate them.

People want to see what the Democrats can do.

Pass legislation in the spirit of constructive democracy, emphasizing substance over partisan rhetoric. Increase the minimum wage in a way that is sensible. An across-the-board hike to $15 an hour isn’t going to fly, and the country will see it as a political stunt. The fact is, no single, national wage can work, because the cost of living from Birmingham to Boston to Baton Rouge varies too widely.

Instead, raise the minimum in each area to a level corresponding to living costs, and index the wage, going forward, to regional inflation. Then tell the country, “We want to raise wages so workers aren’t in poverty, but we recognize that costs vary, and we don’t want to bankrupt businesses.” If Mitch McConnell pretends not to understand, so be it.

Don’t demonize the private sector. Back in the day, first lady Hillary Clinton tried to re-create health care by goring the insurance industry. It flopped. If you want to hold the line on prescription drugs, talk to the drug companies, too.

Regulate Wall Street with particularity, as one would any industry that exists to fill a need and yet is prone to dangerous excesses.

Repeal the carried interest treatment for managers of investment partnerships such as private equity firms and hedge funds. That would include the massively undertaxed and certifiably under-humble Steve Schwarzman, who watched the election returns while whispering unsweet nothings in the ear of his crony, the jefe in chief.

This scandal has gone on too long. Millionaires and billionaires should not pay a lower tax rate than everyone else, so raise it.

Expand the earned-income tax credit, which subsidizes low-wage workers without burdening employers.

Increase taxes not for ideological reasons or to make a point, but to fund the budget. No sense killing the golden goose.

A good place to start: Phase out the mortgage deduction, a giant tax benefit enjoyed (mostly) by wealthier homeowners that is without any economic basis.

A second place: tax all capital assets on the difference between the amount received at sale and the original purchase price, regardless of whether the original purchaser is deceased. At present, the wealthy receive a tremendous break because the “basis” (the original cost) is “stepped up,” for tax purposes, at death.

Logically, there is no reason for death to diminish the eventual tax. By making this change, the inheritance tax, which reaches few estates anyway, could be eliminated.

Expand support for education in the Opioid Belt — that means trade schools, community colleges, state universities. The only long-term answer to income disparity is education.

Reaffirm, in a sense-of-the-House vote, support for the Trans-Pacific Partnership. Explain that with America facing a threat from a mercantilist China, the last thing we should do is alienate our trading partners and allies in Asia.

Narrow the “national security” loophole that allows the president to unilaterally impose import tariffs. That Cold War-era provision was intended to prevent America from becoming dependent for weapons and such during emergencies — not to allow a constitutionally elected public servant to become a trade czar.

Explain to the public that 99 percent of economic policy decisions have nothing to do with national security. By reestablishing a clear line between them, national security will also be strengthened.

Make the same point about immigration. Support legislation to strengthen security, and simultaneously establish a path to citizenship for longtime resident workers and students without criminal records. Expand opportunities for guest workers. Seek testimony from business owners around the country. They will confirm that with unemployment at longtime lows, workers are needed. Don’t fund a wall.

Repeal the 2005 federal law that granted firearms dealers virtual immunity to litigation. The Constitution protects the right to bear arms — not to sell a weapon to a homicidal maniac.

Do a bunch of these things and voters will believe the Democrats are fit and ready. To paraphrase the late Jimmy Breslin, practice the noble art of government.

Don’t run from a fight with the POTUS, but remember, fighting is his element — it’s the only thing that makes him relevant. Nothing can make him look as hypocritical and unappealing as his own behavior.

Investigatory hearings should be focused on specific, identifiable goals. That includes impeachment. As during Watergate, the public will want to see clear evidence of a crime, committed while the officeholder was in power, laid out first.

Hearings that seem overly general, merely political or purposefully contentious are unlikely to impress the part of the public that Democrats need.

If hearings go on too long, or come to define the 116th Congress, then after a while, people will ignore the specifics of what is said. They will come to a general conclusion that the Democrats are oppositional, defined only by what they are not.

That didn’t work in 2016. This time, give the public something to vote for.