RICHMOND, Va. — Former Virginia Gov. Bob McDonnell and his wife are accused of taking at least $165,000 in loans and gifts to help the chief executive of a health supplement company peddle his products. But proving the couple broke the law may be difficult.

Legal experts say the case hinges on whether prosecutors can show that McDonnell agreed provide specific favors in exchange for the gifts, a tough task given the fine line between what is illegal versus what is unseemly. And prosecutors will need to prove the McDonnells abused their positions and conspired together to sell their influence.

“The indictment, as I read it, points to a lot of smoke, but I don’t see any fire,” said Peter White, a defense lawyer and former federal prosecutor in Virginia.

If the gifts-for-favors theory doesn’t stick, prosecutors can still secure convictions if they prove the McDonnells tried to hide the loans and their relationship and dealings with Jonnie Williams, the former head of Star Scientific.

A 14-court indictment Tuesday accused the couple of accepting gifts such as a Rolex watch, a Ferrari ride and a spa resort vacation. Prosecutors said the couple in turn promoted Star Scientific’s products and gave special treatment to Williams, including arranging for him to meet a state health official. The couple also opened up the Executive Mansion for a launch party for the company’s signature product.

An arraignment and bail hearing is set for Friday.

The McDonnells and their attorneys have launched a counteroffensive, saying the former governor and first lady did nothing for Star Scientific that they wouldn’t have done for any other company.

The gifts weren’t bribes, McDonnell’s lawyers said, because the governor never gave Williams anything that wasn’t a routine courtesy doled out by every politician.

McDonnell’s legal team focused on gifts received by U.S. Sen. Tim Kaine, a Democrat who was Virginia’s governor from 2006 to 2010. According to court records and published media accounts, those gifts included use of a private Caribbean island called “Mustique” from James B. Murray Jr., an investor who Kaine reappointed to a state commission on higher education board appointments.

A Kaine spokeswoman said the senator was confident he followed ethics laws.

The defense said the decision to charge McDonnell was not much better than the Roman Emperor Caligula, who “imprisoned people for violating laws written in tiny lettering on a pillar too high to see.”

One problem for prosecutors may be showing McDonnell took official actions to help the company. Courts have generally understood this as introducing legislation or ensuring a person or company is awarded a contract, White said. Arranging a meeting, or hosting an event, don’t fall into the same category, he said.

“If it is the case that hosting an event at the governor’s mansion is an official act, which I guess they believe is the case, that’s going to change how politics is practiced wildly in the country,” White said.

McDonnell, a once rising star in the Republican Party who had been seen as a possible running mate for Mitt Romney, was limited to one, four-year term and left office earlier this month. The investigation has crippled his political future and sullied the reputation of a leader who had won praise for bipartisan appeal.

The indictment portrays Maureen McDonnell as a central driver in the relationship, telling Williams, for instance, that she needed a dress for the inauguration and asking him to buy a Rolex watch her husband. Her lawyers can argue that as an unelected official, she didn’t have any direct executive power, though prosecutors may have overcome that hurdle by charging the McDonnells together in a conspiracy.

Several counts of the indictment were brought under the anti-fraud “honest services” law, which the Supreme Court in 2010 weakened considerably in the case against former Enron CEO Jeffrey Skilling. The court appeared to limit the law, which defense lawyers had long criticized as overly vague, to cases where bribes or kickbacks were paid.

“Clearly, if the government can tie a gift to an expectation with respect to a specific act, that is going to be sufficient to make out the charge of honest services,” said Barry Pollack, a white-collar defense attorney in Washington. “But if all they’re able to do is to show that when the gifts were made, Gov. McDonnell intended that he would provide some general consideration in return – but no specific act was in mind – that may or may not be sufficient.”

Barbara Van Gelder, a criminal defense attorney, said a quid-pro-quo doesn’t have to be a direct exchange if prosecutors can show that a “stream of benefits” intended to influence actions changed hands.

“They don’t have to say that on ‘x’ day, my kids went golfing, and 2 days later, I let them use the governor’s mansion. It can be far more amorphous than that,” she said.

Apart from the quid-pro-quo theory, prosecutors accused Maureen McDonnell of lying to investigators about the date she met Williams. She also tried to impede the investigation by sending Williams a handwritten note to make it appear as if they had a standing agreement for her to return certain luxury gifts, the indictment said.

The former governor is accused of failing to disclose loans from Williams on loan paperwork.

Such charges, typically less cumbersome to prove than outright bribery, are useful for the government to argue a pattern of dishonesty. Or they can help convince a jury that there are grounds for some sort of conviction in cases where juries “don’t want to let these people walk completely,” said defense lawyer William Lawler.