One great advantage of electing a governor as rich as Phil Murphy, we were told, is that he could not be bought. With his own chest full of gold coins, he would never need to scrape and beg for help from special interest groups seeking his favor.

But it hasn't worked out that way. A month after his election, Murphy's senior political team opened a dark money fund and began soliciting donations.

It came as a surprise, since Murphy had promised to bring new transparency to Trenton, and the identity of the new donors was kept secret, along with how much they gave. To quiet the critics, Murphy's campaign manager and senior advisor, Brendan Gill, who helps manage the fund, promised to come clean by the end of 2018 and reveal the identity of the donors.

They just broke that promise. So, today, special interest groups are giving money to Murphy's cause -- no doubt because they expect him to do their bidding -- and the public has no clue who they are.

Is the money coming from public worker unions who negotiate contracts with Murphy? Is it coming from marijuana firms that are scrambling to shape the law legalizing adult sales? Is it coming from law firms that have contracts with the state government? They won't say.

It gets worse. Murphy himself has been soliciting money for this group, according to three sources with direct knowledge of his efforts. "He called me on Nov. 28 and asked me if I could contribute," said one of them, a union official who requested anonymity.

The federal law governing this type of group, known as a 501c4, prohibits the governor from directly managing the organization. But that legal separation is farcical. Murphy has appeared in TV ads the group bought, and he solicits the money. The buck stops with him.

On Friday, four days after this news broke, Murphy finally said he believes the donors should be revealed. But he would not confirm or deny that he has been soliciting donations. That's called stonewalling.

What is Murphy hiding? He has to know that breaking this promise damages his reputation. So, his team must believe that opening these books would do even greater damage.

The official explanation for the secrecy is ludicrous: "Our supporters have come under increased attacks from powerful special interests seeking to preserve the status quo in recent months," said Phil Swibinski, a spokesman for the organization, New Direction New Jersey.

Really? They've come under attack, even though their names haven't been revealed? How does that work?

This is another inexplicable rookie mistake by Murphy and his senior team. Until they come clean, they should at least spare us the happy talk about bringing a new brand of politics to New Jersey. This smells just like the old brand.

More: Tom Moran columns

Tom Moran may be reached at tmoran@starledger.com or call (973) 836-4909. Follow him on Twitter @tomamoran. Find NJ.com Opinion on Facebook.