When Newsday endorsed Shirley Republican Lee M. Zeldin in his 2014 run to unseat Democratic Rep. Tim Bishop, the fact that Zeldin could have the power to help Eastern Long Island as a member of the dominant Republican majority was a prime reason.

The GOP wanted the seat badly. It had repeatedly and unsuccessfully targeted Bishop. Once the party won the district, Zeldin should have had power. He should have been willing and able to make the case that he’d have to take care of the voters’ needs and perch on the party’s moderate wing if he wanted to keep the job and fairly represent his diverse district.

Zeldin didn’t do either. Instead, he embraced an extreme brand of conservatism, and failed to secure some crucial Long Island needs.

Then he got worse.

President Donald Trump came on the scene and Zeldin quickly became a reliable cheerleader for Trump’s divisive, dismissive politics and disastrous policies. Most troubling are Zeldin’s feverish efforts to discredit the federal investigation into Russia’s involvement in the 2016 election. Zeldin joined with the most right-wing elements of his party, even speaking on the House floor in a #releasethememo campaign. More recently, he sponsored a bill to create a second special counsel to investigate the FBI’s probe of Hillary Clinton’s emails.

Zeldin, 38, says a top priority is the preservation of Plum Island, which hosts a federal animal disease research center just off Long Island. The lab’s functions are moving to Kansas, and federal law requires that it be sold to the highest bidder, which would likely lead to commercial development. That’s an unacceptable outcome. The prospect led the Town of Southold to pass zoning laws making the island essentially impossible to develop. But zoning can change. Federal protection is needed.

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This is exactly the kind of local need a majority-party legislator with power in his caucus and the ear of the president ought to be able to satisfy. But Zeldin has gotten nowhere. His bill to stop the sale and have the government draw up a plan to preserve and protect Plum Island has passed in the House more than once but gone nowhere in the Senate. Plum Island has no more federal protection today than the day Zeldin was elected.

The same is true of 1st District residents who bought their homes counting on federal deductions for state and local income and property taxes. Those long-standing deductions were limited to $10,000 annually in a tax bill Republicans passed last year. That added $1.5 trillion to the deficit and used the loss of Long Island homeowners’ deductions to help pay for a huge corporate tax cut. To his credit, Zeldin fought limiting that deduction. To his detriment, no one listened.

In perhaps his worst vote in four years, Zeldin joined his party’s efforts to repeal the Affordable Care Act. Except for the courage of the late Sen. John McCain, who defeated the effort in the Senate, as many as 1 million New Yorkers could have lost Medicaid benefits over time and more than 60,000 1st District residents could have lost their insurance.

Zeldin is often vocal. Up until the time he had to protect his seat in a swing district, he had been a regular on cable channels, lambasting the investigation into Russian interference in the 2016 election. He made his voice heard fighting for billions of dollars in cuts to Environmental Protection Agency funding.

And he’s a leader in the crusade to gift the National Rifle Association with a 50-state reciprocal concealed-carry weapon law. Such a change would give anyone legally allowed to carry a concealed semi-automatic handgun — and in at least 13 states there are essentially no requirements to get such permission — the right to conceal and carry such weapons in New York and in his district. That would mean a gun right that is extraordinarily difficult for Zeldin’s own constituents to obtain, thanks to reasonable state and local legal restrictions here, would be freely granted to millions of unscreened out-of-staters.

Perry Gershon, 56, of East Hampton, is a successful financier spurred to get into the race by the election of Trump, and by Zeldin’s support for Trump’s policies. This has prompted Zeldin to repeatedly criticize Gershon for only recently moving his voting registration to Suffolk County from Manhattan, although he’s owned a home in the district since 1999 and has spent considerable time there, and before that with his wife’s family. It is a legitimate criticism.

But not being a native and wanting to stand up for residents of the 1st District is better than being from the 1st District and repeatedly letting them down. Gershon is smart, motivated, tireless and a listener, and his is the kind of private-sector success story many conservatives want to see more of in government. He says he has driven his blue Chevy Volt more than 38,000 miles across the district to meet with voters since the campaign started.

Gershon has made fighting climate change central to his campaign. Zeldin stands against policy changes that would keep rising waters and increasing storms from swallowing the district.

Gershon wants to strengthen the Affordable Care Act and push for a public insurance option all Americans can buy into, and thinks the nation could get to single-payer health care over time. Zeldin and his allies weakened the law in a way that over time will drive up rates for New Yorkers who need coverage most.

Gershon wants to give people brought illegally to the United States as children a path to citizenship. Zeldin staunchly opposes such a path.

Gershon wants a huge increase in infrastructure spending. Zeldin and his party pay that priority lip service, and do nothing to bring it about.

Gershon wants to act as a brake on Trump. Zeldin’s support enables the president’s worst behaviors.

Gershon promises to be a strong voice trumpeting the right policies for the district and the nation. Zeldin has been a voice for neither.

Newsday endorses Gershon.

Editor’s Note: Perry Gershon drives a Chevy Volt. The model of his vehicle was misspelled in an earlier version of this editorial.