In a Facebook post on Wednesday, Mitt Romney discussed the fact that Donald Trump has vowed that he won t release his tax returns before the election. Romney insists that Trump must have a  bombshell  in his tax returns and that they might reveal something really nefarious and  disqualifying. This statement was in response to the bombshell Trump dropped on voters on Wednesday, in which he said he wouldn t release them. Trump has previously said that he would release his tax returns once the IRS is done auditing them. This claim is bizarre on its face. Here s Trump during a debate talking about the alleged audit:Tax experts are dubious:An audit by itself would not prevent Trump from releasing his tax returns, said David Cay Johnston, a Pulitzer prize winning tax author. It is up to an individual whether to disclose his or her tax return to the public, a lender or anyone else who wants to see it.Audits are rare. Overall, fewer than 1% of all individual returns are audited, although the rate is closer to 10% for tax filers with incomes over $10 million. The IRS says it expects to conduct 1.2 million individual audits this year, the lowest level in 11 years.Source: CNN MoneyThe IRS agrees: Federal privacy rules prohibit the IRS from discussing individual tax matters. Nothing prevents individuals from sharing their own tax information,  the IRS said in a statement released to NBC News.Source: NBC News Originally, the speculation was that Trump s tax returns would show that he s worth far less than his claim of $10 billion (or whatever he s saying today), but apparently Romney feels that it could be something much, much worse, and that Trump might have ties to the mob. Of course, that s not a huge leap to make, especially since Trump is in the construction business and in the casino business. Both industries are known for mob connections. That doesn t mean he has the mob connections, or more importantly, that he benefits from the mob connections, but it s not surprising that Romney could draw that conclusion.The irony, though, is that the tables have done a complete 180 from 2012 to now. Four years ago, Romney hadn t yet released his tax returns and it was Trump calling for transparency. Here s Romney being asked about his tax returns:Trump did eventually endorse the multi-millionaire, but not after saying this about Romney s tax returns:I think Mitt was hurt really very badly by this whole thing with the income tax returns. I believe he should have given them April 1, but I didn t think going into a little bit of detail without going into a lot of detail was positive thing. He ll come back. He has proven to be very resilient guy. He has been hurt a number of times by number of different things, he comes back. He really seems to be very tough and resilient. You have to hand it to him.Source: Fox NewsIt s somewhat surprising that Trump won t release his tax returns. He has famously said that he could shoot someone from the middle of Fifth Avenue and his followers would still love him. Sadly, that s probably true. A few billion less on his tax return can t make a difference, right? It s doubtful that even mob connections could damage him politically. Even white supremacist connections make his followers say  meh.  It could be that Trump s tax returns have something much worse, for him. They could point to illegal activity. This could be mob related, or it could be something else.Featured image via Ethan Miller/ Getty Images.