Gov. Chris Christie wasn’t willing to give up the New Jersey statehouse to be Mitt Romney’s running mate because he doubted they’d win, The Post has learned.

Romney’s top aides had demanded Christie step down as the state’s chief executive because if he didn’t, strict pay-to-play laws would have restricted the nation’s largest banks from donating to the campaign — since those banks do business with New Jersey.

But Christie adamantly refused to sacrifice his post, believing that being Romney’s running mate wasn’t worth the gamble.

“[Christie] felt, at one point, that [President] Obama could lose this. And, look, there still is that chance. But he knows, right now, you have to say it’s unlikely,” one source said.

The tough-talking governor believed Romney severely damaged his campaign by releasing only limited tax returns and committing several gaffes during his international tour in July.

Certain Romney was doomed, Christie stuck to his guns — even as some of his own aides pushed him to run, another source said.

“There were people around him that wanted him to reconsider, to actually push to be vice president. But he’s known there are real issues here. Chris knows the score,” the source said.

His problem was two Securities and Exchange Commission rules that are meant to curb pay-to-play.

One rule, enacted in the mid-1990s, restricts Wall Street executives whose firms underwrite municipal bonds from making personal contributions of more than $250 to a governor running for federal office — or risk being banned from doing business in that state for two years.

That severely limits banks like Goldman Sachs, JP Morgan Chase, and Citibank from donating to a Romney-Christie ticket if Christie remained governor because they do business with New Jersey.

The second rule, enacted in 2010, limits pension-investment advisers from making campaign donations to a governor running for federal office.

That would have restricted powerhouse firms like Morgan Stanley, Lazard and Wellington Advisors from contributing, because they also do business with New Jersey.

Romney officials were wary of losing those potential donations — especially as Obama struggles to get Wall Street dollars.

But “Christie refused to resign under any circumstances,” a Romney source said. “It had nothing to do with Chris’ personality and everything to do with money.”

Christie’s aides tried to find a way around the rules — like passing off power over state bonds and pensions to another official.

But that didn’t satisfy Romney officials. They feared that if Christie ran for veep and didn’t resign, the Obama campaign could challenge any Wall Street donations.

“The Romney campaign really wasn’t taking any chances,” another source said. “The law affects sitting governors more than anybody.”

Also, banks and advisory firms feared getting hit with penalties if they contributed to the campaign.

“These are serious potential penalties that could cost a company millions,” said campaign-finance lawyer Ken Gross, of Skadden, Arps in DC.

“There’s no recusal. It’s the authority of the office. You can’t just say, ‘I’ll let a deputy make those decisions.’ ”