When their far-fetched, marriage-gone-bad defense failed to save former Virginia Gov. Robert McDonnell and his wife, Maureen, from guilty verdicts in their corruption trial, I could not help but wonder: Why didn’t they take a plea deal when they had the chance?

Federal authorities had offered to avoid charging the state’s first lady if the then-governor pleaded guilty to one felony fraud charge.

But the governor rejected the offer, and the couple was jointly charged with trading on his office to help businessman Jonnie R. Williams Sr. and his company, Star Scientific, sell a nutritional supplement called Anatabloc, made from tobacco derivatives. Sounds yummy.

Now both McDonnells have been found guilty by a federal jury in Richmond. The ex-governor was found guilty of 11 corruption-related counts and the former first lady was found guilty of eight counts.

They face time in federal prison when Judge James R. Spencer sentences them Jan. 6.

Accepting the plea deal probably would have meant the former governor would have spent little time in prison, if at all. It also would have spared the McDonnells and their children the humiliating soap opera that unfolded in their bad marriage defense.

For nearly two years, authorities charged, the McDonnells used Mr. Williams as a personal ATM for loans and gifts of money, clothes, golf fees and equipment, trips and private plane rides totaling more than $165,000.

In exchange, the McDonnells allegedly worked together to sell the prestige of the office that, as Virginians are quick to point out, once was occupied by Patrick Henry and Thomas Jefferson.

Their defense? Lawyers argued that the two were barely on speaking terms, so the governor could not have known that Mr. Williams had paid for such gifts as, for example, a $15,000 high-fashion New York shopping spree for Mrs. McDonnell or a $6,500 Rolex watch she gave Mr. McDonnell as a Christmas present.

Nor could the governor have known about actions she took to help Mr. Williams promote his dietary product, the defense claimed.

But the blame-the-wife narrative crumbled in contradictions over how much of that largesse was for the governor, including sweetheart loans and other contacts that the governor described as “routine” access to government.

So why didn’t the governor take the plea deal? Having witnessed way too many other politicians whose rising stars flamed out in a stunning scandal, one word came to my mind: Hubris, the belief that you’re too clever and wonderful to have to care about the rules.

As a successful lawyer and politician who was on Mitt Romney’s short list of vice presidential hopefuls, Mr. McDonnell fell prey to a common political pathology: The earnest belief that he could charm his way out of any mess.

It worked for President Bill Clinton, who survived impeachment.

But it did not work for eight other governors who have been convicted in the past 15 years, including Illinois’ Rod Blagojevich, a Democrat who was sentenced to 14 years in 2011 for trying to sell President Obama’s seat in the U.S. Senate.

Virginia traditionalists like to cite the “Virginia Way” as better than the “Chicago Way,” a popular nickname for the politics in President Obama’s adopted hometown. Virginia didn’t have any current or former governors indicted before Mr. McDonnell. But, as his case reveals, that’s partly because Virginia has some of the most lax ethics laws in the nation.

For example, according to the National Conference of State Legislatures, Virginia is one of just 10 states that allow officeholders or their relatives to take personal gifts of unlimited value. Mr. McDonnell promised ethics reform as a candidate, then dropped the issue after being elected governor. Is the Virginia Way all that much less corrupt or do they only have looser rules?

It is my hope that politicians nationwide take the McDonnells’ convictions as a wake-up call: Voters may be getting even more fed up than usual with rule-bending politicians.

Those politicians who impress voters with their charm on Election Day for the ballot box may face a much tougher challenge with the jury box.