Tuesday’s detailed federal indictment of Virginia’s former first couple helps to answer a baffling question: How did a smart guy like Bob McDonnell end up in this mess?

There’s no single explanation. But the 43-page document leveling corruption charges against the former governor and his wife, Maureen, provides a compelling narrative.

In it, we see a man brought down, at least politically, by a toxic mix of personal money worries, an assertive wife, a taste for luxury, and a culture of coziness between politicians and rich supporters.

Also, and perhaps most important, we see a man in denial. As a veteran politician, he knew he risked major embarrassment if the $165,000 in gifts and loans from businessman Jonnie Williams Sr. became public.

That’s why McDonnell (R) took several steps to conceal how much he and his family had received from Williams. For instance, the indictment alleges that McDonnell arranged with Williams in March 2012 to transfer $50,000 as a check rather than as stock, because the latter would have to be disclosed.

But McDonnell rationalized his behavior on the theory that his actions were technically permitted under Virginia’s highly forgiving gifts and disclosure laws.

By this logic, it was fine to accept $15,000 from Williams for a reception at his daughter’s wedding, or $19,000 in designer clothes and accessories in a New York shopping spree for Maureen. After all, gifts to family members didn’t have to be disclosed.

Likewise, it was okay to urge the state bureaucracy repeatedly to look into how it might help Williams market his company’s new diet supplement. After all, governors help promote state businesses all the time.

McDonnell’s mistake was overlooking the danger that federal prosecutors would draw a connection between the two and accuse him and Maureen of trading one for the other.

That kind of hairsplitting is typical of McDonnell. As a legislator, state attorney general and governor, he was known for obsessing over minor points of legislation and policy.

Of course, a jury might clear McDonnell. But two problems weaken his defense.

First, the indictment describes a pattern of suspicious coincidences of timing. Again and again, shortly after the family received a gift or loan from Williams, one of the McDonnells or the governor’s office sent an e-mail or took another action designed to help Williams’s company.

That makes it harder for Bob McDonnell to argue that he wasn’t doing anything special for Williams.

Second, although previous governors accepted jet trips or luxury vacations from rich donors, McDonnell broke with past practice by accepting $120,000 in loans. So it’s harder for him to argue that “everybody did it.”

The indictment shows that the McDonnells were secretly worried about their personal finances when Bob was inaugurated as governor in early 2010. Maureen wrote in an e-mail then that her husband was “screaming about the thousands I’m charging up in credit card debt.”

The indictment also details how Maureen repeatedly took the lead in prodding Bob to take advantage of Williams’s generosity.

Williams’s largess didn’t just help the couple keep up payments on ill-timed real estate investments. It also enabled them to enjoy luxuries to which they felt entitled by virtue of Bob’s office.

These included a fancy vacation in Cape Cod; Louis Vuitton shoes and purses for Maureen; and a $2,380 golf excursion for Bob, his two sons and a future son-in-law.

Maureen often solicited help from Williams without Bob’s knowledge, according to the indictment. In January 2012, an e-mail shows, the governor wasn’t aware that his wife had gone to Williams for assistance in covering one of the real estate debts.

“Maureen who are we talking about that is helping us?” he wrote to her.

Maureen doesn’t get all the blame, however, because ultimately Bob went along. A month after sending the 2012 e-mail, he allegedly was meeting with Williams to arrange what became the $50,000 loan, without paperwork.

Finally, the whole affair highlights the damage done when politicians depend on wealthy contributors for travel, socializing or other help. Bob McDonnell first met Williams during the 2009 gubernatorial campaign after somebody on McDonnell’s staff asked the businessman to make available his private jet for the candidate’s use.

The scandal is supposed to mean the General Assembly will put more teeth in the gifts and disclosure laws. Let’s hope so.

Bob McDonnell’s case shows it isn’t safe to rely just on a politician’s conscience.

I discuss local issues Friday
at 8:50 a.m. on WAMU (88.5 FM).
For previous columns, go to washingtonpost.com/mccartney.