With rail’s future uncertain, former Hawaii Gov. Ben Cayetano took out a full-page ad in Friday’s Washington Post appealing directly to President Donald Trump to halt federal spending on the project.

The ad, paid for by the Abigail K. Kawananakoa Foundation, asks Trump to withhold the $800 million or so left in the Federal Transit Administration’s $1.55 billion full funding grant agreement with Honolulu, a move that Cayetano says would compel the city to “seriously consider some of the less costly alternatives to complement the rail system.”

The ad notes that rail’s estimated costs have nearly doubled in recent years, rising from about $5.26 bil-lion (Cayetano puts it at $5.28 billion) when the federal deal was inked in 2012 to a price tag approaching $10 billion when the financing and costs to pay off interest are included.

“Honolulu’s rail project does not deserve a single dollar more from the federal government,” Cayetano’s signed ad states. “It has become a poster boy for how politics, incompetence, disinformation and outright lies are at the root of wasteful rail projects which do little for the public except raise taxes.”

The ad, in one of the nation’s largest newspapers, looks to upend the local 20-mile, 21-station project at one of the most critical and precarious junctures in its history. With the cost increases, the project is said to be about $3 billion short of what’s needed to finish it, and state lawmakers are weighing another extension of Oahu’s general excise tax surcharge.

The city and its rail agency also face an April 30 deadline to give the FTA a “recovery plan” on how they aim to deal with the funding gap and still build a viable transit system. They’re hoping another GET extension will mostly help fix that challenge.

If the FTA doesn’t accept whatever plan the city submits, it could revoke the $1.55 billion.

Cayetano, who led the Aloha State from 1994 to 2002, is a longtime opponent of the controversial project. In 2012 he ran unsuccessfully for mayor on an anti-rail platform against Mayor Kirk Caldwell in a bruising general election race that sometimes resembled a referendum on rail.

“The people of Oahu have now gone through three election cycles where rail was the issue of the day, and each time affirmed that rail should be completed as originally planned,” Caldwell said in a statement released by his office Friday reacting to the Post ad.

Rail opponents have released similar ads in each of those election cycles, Caldwell said. He added that he remains focused on getting another tax extension passed to complete rail to Ala Moana Center.

Kawananakoa, meanwhile, funded a lawsuit against the city in recent years challenging the validity of City Council votes for the transit project, arguing that members had not publicly disclosed conflicts of interest.

Her ad with Cayetano was published Friday as state House and Senate members enter their end-of-session conference meetings to hash out what, if anything, they’ll do about rail.

At Thursday’s rail board meeting, project officials announced that Sens. Jill Tokuda (D, Kailua-Kaneohe), Lorraine Inouye (D, Kaupu-lehu-Waimea-North Hilo), Clarence Nishihara (D, Waipahu-Pearl City) and Donovan Dela Cruz (D, Wahiawa-Whitmore-Mililani Mauka) were chosen to be the Senate’s rail conferees, while Reps. Sylvia Luke (D, Punchbowl-Pauoa-Nuuanu), Henry Aquino (D, Waipahu) and Bob McDermott (R, Ewa Beach-Iroquois Point) will represent the House in those talks.

That conference group includes both rail-friendly legislators and others who have expressed deep reluctance to pass another rail tax extension. Meanwhile, Caldwell introduced a bill Wednesday to the Honolulu City Council to approve such an extension. (The city — not just the state — needs to approve the extension for it to take effect.)

Cayetano said he started drafting a letter to the Trump administration about a week ago when state Capitol sources told him lawmakers might not “hold the line” on limiting rail funds and that the legislators were considering a 10-year extension of the half-percent surcharge that would push it to 2037.

When Kawananakoa heard Cayetano was drafting a letter, she offered to have it published as an advertisement, Cayetano said.

“I said, ‘Wow, OK,’” Cayetano recalled Friday.

He said he hopes that Trump’s new transportation secretary, Elaine Chao, will consider his request but that he hadn’t heard anything back yet.

The Cayetano ad further includes the renderings of rail’s elevated guideway prepared several years ago by the Honolulu chapter of the American Institute of Architects that show substantial impacts to views and the corridor along the Honolulu Harbor waterfront.

“If built, this will change the beauty and ambience of the city forever,” the ad reads.

The local AIA previously opposed the plan to run elevated rail in town. More recently, however, the group has declined to take a position because it polled members last fall and found “there was not … a largely agreed-upon position,” according to AIA Honolulu Executive Vice President Abigail Mundell.

The city estimates that rail will annually cost nearly $130 million to operate in 2026 and that the system will see 119,000 daily trips in 2030. Cayetano said he’s concluded Honolulu is too small a city to support a transit system of the project’s size. He further said the state should be focusing on issues such as affordable housing and education instead.

However, rail advocates say that the elevated transit line will help ease the island’s affordable-housing crisis by providing more units along the route.