Mayor Kirk Caldwell was brought into Honolulu Hale by former Mayor Mufi Hannemann and although they are not a team today, they remain linked by a rail project steadily growing more expensive and controversial.

Finishing paying for rail, now estimated to cost up to $9.5 billion, will be Caldwell’s top job, he said during his second-term, swearing-in ceremony last week.

Of course, Caldwell knows that trains won’t run on those expensive tracks for about nine more years, but today he will still have to answer the questions.

Plans on how to finish and how to pay for it seem to change with the month. While Caldwell has proposed city partnerships with developers and landowners along the 20-mile route, no one has agreed to anything except lining up taxpayers to pay.

In fact, the latest plan growing legs is one boosted by state Sen. Will Espero, which would extend or make permanent the 0.5 percent general excise tax increase with some of the extra money going for state transportation projects.

Precisely who would pay — Oahu residents, as is now the case, or everyone in Hawaii — is still a question.

Caldwell has also said he would think about switching rail funding to long-term bonds, which would stretch out the payments over decades, but would result in taxpayers paying millions more in interest costs.

Other politicians are also thinking about the political costs they will be paying. There may be other reasons, but Mufi Hannemann has not won an election since he successfully talked the state Legislature and the City Council into the rail project, which was then estimated to cost about $3 billion.

It will be Caldwell who leads the city’s team to the Legislature this year and it appears that it will be Caldwell who stands to get the credit or blame for whatever is the final product.

Everyone is under a deadline to get something approved by April 30 under the latest federal edict.

There is a final political equation for Caldwell to solve: Perhaps not by April, but sometime in the future, Caldwell must plan out his own political future.

His term of mayor extends to 2020, but there is a big race for governor next year. Running for governor in the last two years of one’s last term as mayor is always a great temptation.

For instance, Caldwell first became mayor when as managing director he stepped into the job when Hannemann resigned to run for governor.

During the campaign Caldwell said he was running to serve a four-year term, but politics is all about maintaining your options. Interestingly, one of Gov. David Ige’s shrewdest political moves was his endorsement last year of Caldwell over former Congressman Charles Djou in the race for mayor.

Measuring by political appearances, for Caldwell to now run against Ige would be the definition of tacky.

It also would not help with any city-state cooperation or even rail funding.

All that leaves Caldwell with four years to steer an uncertain and costly train project with questionable political benefit, and a political future marked “to be determined.”

Richard Borreca writes on politics on Sundays. Reach him at 808onpolitics@gmail.com.