How bad could this presidential campaign get? Here's how bad: We could swerve into third-world, a la the likes of Ukraine, if President Obama persists in charging Mitt Romney with criminal behavior.

He needs to end this line of accusation now. Going that far is wrong, and the president needs to say so. So does Obama spokesperson Stephanie Cutter.

Here’s why: Obama is not just a candidate for office. He is the president of the United States. He is the chief law enforcement officer in the land. That gives his public utterances — and those of his surrogates — real heft.

By suggesting violations of law, the question arises: Do his accusations mean that he will have the Justice Department or the Securities and Exchange Commission investigate Romney for the crime that he has accused him of? What does the president plan on doing about the alleged crime that his organization says it has discovered? Or, will this be another example of the president's selective law enforcement?

Certainly, that's the specter he raises. And that’s the line that is being crossed — and shouldn’t be — in this latest escalation in political speak.

Can the president taunt his opponents with the threat of criminal charges? Is he going to have his government act on his assertions? Is that how low Obama is willing to take American politics? Can a president threaten or even investigate his opponent as a way to win reelection? Put politely, the president needs to put up or do the opposite.

I’m exaggerating to make a point, I hope. But Obama needs to reassure America about what he thinks his powers can be used for — and what they cannot be.

Serious people, journalists, political officials, government leaders and private opinion leaders need to call Obama out on this sorry episode. They need to reject this kind of politics. Otherwise, we start down a very long slide.