As a far-right candidate in Wisconsin last year, Ron Johnson spent about $9 million of his own money to buy a Senate seat he had no business winning. What we didn’t know until today is that Johnson received $10 million in deferred compensation from his plastics company shortly after his election.

It’s raising uncomfortable questions for the dim-witted Republican.

The first-term Republican declined to say how his Oshkosh firm, Pacur, came up with a figure that so closely mirrored the amount he personally put into his campaign fund.

“You take a look in terms of what would be a reasonable compensation package, OK?” Johnson said this week. “It’s a private business. I’ve complied with all the disclosure laws, and I don’t have to explain it any further to someone like you.”

“Someone like you,” in this case, is a journalist asking a fair question. What will be more interesting, however, is whether Johnson is more cooperating in answering questions from federal investigators. The head of the Wisconsin Democracy Campaign called for an FEC probe, noting that the $10 million in deferred compensation “looks like a scheme to get around a century-old law” that prohibits corporate donations to candidates. “It’s a clever scheme, but it still looks like a scheme to get around the law.”

For his part, Johnson sees this as a coincidence. Before the election, he spent $9 million, and then after the election, he arranged for his company to give him $10 million. But there’s nothing untoward about any of this, because the payoff was “an agreed-upon amount.”

Agreed upon with whom?

“That would be me,” Johnson said, suggesting he picked his own payoff.

I’ve feared for a long while that Johnson just isn’t very bright. He was a far-right candidate who railed against government intervention in private industry, but has sought and received federal aid for his business enterprises. He thinks “sunspots” cause global warming, which doesn’t make any sense. He’s argued that China is better for businesses than the United States. He thinks Greenland has snow because of global cooling. At the height of the BP oil spill disaster, he said he’d sell his BP stock, just as soon as it was more profitable for him.

And as an actual member of the Senate, Johnson has actually been slightly worse.

But this new story is more serious. Having a limited intellect is one thing; being corrupt and circumventing election laws is something else.

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Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.