Construction of Oahu’s fixed-rail system has been seen as the focal point of the city’s urban planning for decades to come.

The 20-mile route, linking East Kapolei with Ala Moana Center, was to become the spine of a multimodal transportation system enabling more efficient travel to destinations. It would have provided the magnet for development that would yield thousands of needed housing units along the central commuting corridor rather than generating more urban sprawl.

Now Mayor Kirk Caldwell, in a startling and disappointing about-face, on Thursday joined in with a chorus calling for the “solution” that makes no sense in the long term: halting the system at Middle Street, five miles from the intended terminus.

This amounts to jumping on a bandwagon — joined by a range of state lawmakers, City Council members and other politicians — signifying nothing less than abject failure of leadership and lack of commitment to a system that Honolulu needs.

Yes, faulty cost projections have plagued this project, but it’s the shockingly high contractor bids that are dooming rail as well. A hot construction market should not enable unbridled profiteering that leaves taxpayers, and the next generation, with a pathetic rail system that stops far short of its most popular intended destinations.

Caldwell hedged his position on Friday, asserting that continuity of the project would not necessarily be broken. The mayor pledges to secure other funding to complete the full alignment as designed, proposing to seek it from federal, state and private sources. But there’s no indication that this money will materialize in time to keep construction on track, or ever.

The only thing that is clear is that, as described, the project will end at a point where it’s projected to lose about half its ridership. Commuters won’t flock to ride the rail if, at Middle Street, they’ll have to disembark and wait for a bus to their urban-core destination.

That result wouldn’t justify the investment Honolulu’s taxpayers already have made.

Then, once the forward drive to complete the project is allowed to stall out, inertia would settle in. When the project is finally completed — if it ever restarts — the full pricetag would be higher than it would be if the city stuck to the current plan. That much is certain.

There’s political expediency in this decision. Caldwell is facing a tough re-election battle. One of the leading contenders, Charles Djou, already has positioned himself as opposed to spending more money on rail than the current funding mechanism, a half-percent surcharge on the state general excise tax, will provide.

Not wanting to abandon the mantle of fiscal responsibility, the mayor clearly felt pressure to act.

To be sure, Caldwell — elected on a platform of building rail better, back before costs began skyrocketing — is backed into a corner by other factors.

In addition to $1.55 billion in pledged federal funding, the city expects the GET to produce the balance of a $6.8 billion pricetag for the project. Meanwhile, cost estimates from the Federal Transit Administration put the bottom line at $8.3 billion.

The Honolulu Authority for Rapid Transportation, the agency building the project, now faces an Aug. 7 deadline for giving a “recovery plan” to the FTA, proposing how it would complete the project with current funding.

At its Thursday meeting, the mayor told the HART board that the only alternative plan that could be submitted by that deadline with any cost-covered confidence was the Middle Street halt. That might be a correct calculation, but it’s not a solution.

What Oahu’s traffic- jammed residents needed to hear was a clear explanation of why this rail project is necessary and some realistic thinking about funding sources. That would demonstrate a level of commitment lacking in Caldwell’s current posture.

Private partnerships, for example: Yes, those could work. How about some models describing private partners sharing in the cost of completing rail stations that serve their properties? Ala Moana Center, for example, will certainly benefit from being the end destination. Surely its owners could participate in realizing the project.

State funding: Yes, lawmakers should revisit authorizing further extension of the GET surcharge. Legislators quailed at extending the tax authority for even five years, and the City Council approved it, after a prolonged, nervous hesitation. This is a project that demands more political courage than that, from all players.

Lastly, this message to the construction industry: Completion of a once-worthy project is now in doubt, which means that, after all, the sky is not the limit on how high the bids can go.

Profit-making in a hot construction market is a given. But this is a project the weary commuters on clogged freeways need desperately. It’s one on which the future productivity of the city depends.

Putting all that at risk will be a loss, ultimately, for everyone.