Since mid-May, President Obama and his campaign have been attacking Mitt Romney for "shipping U.S. jobs overseas." They've suggested he made false filings to the Securities and Exchange Commission. And they've hit him for having "Swiss bank accounts and offshore investment funds in the Caymans." Before considering their political impact, let's review each of these charges.

The first allegation—that Mr. Romney "shipped jobs to China and Mexico"—was called "misleading, unfair and untrue" by the Washington Post fact checker and labeled "bunk" in an editorial. The Annenberg Center's said it "found no evidence to support the claim that Romney...shipped American jobs overseas."  Neither has anyone else. But Mr. Obama has not backed down, with his campaign spending more than $30 million to run TV ads on the subject for nearly three months.

The second charge—with its implied suggestion that perhaps Mr. Romney should be in jail rather than running for president—came in a July 12 conference call. Mr. Obama's deputy campaign manager, Stephanie Cutter, accused Mr. Romney of "misrepresenting his position at Bain" to the SEC, "which is a felony."

Three days later Mr. Obama doubled down on the incendiary charge during an interview on WAVY-TV in Portsmouth, Va. He personally attacked Mr. Romney for saying he left Bain's leadership in 1999 while, during the subsequent three years he spent running the Olympics, signing "an SEC listing that says he was the CEO, chairman, and president of the company." What the president didn't say was that this is a customary practice for CEOs who take a leave of absence from their firms. This is precisely the reason that found the president's charge misleading while the Washington Post said the "facts essentially exonerate Romney."

Consider another high-profile CEO: In January 2009, Steve Jobs took a leave from Apple for health reasons. But like Mr. Romney, Jobs later signed SEC documents listing him as CEO, even though he'd relinquished day-to-day control of the company to Apple's chief operating officer. Maybe a reporter should ask Mr. Obama if he believes Jobs was a felon.

Then there are the attacks on Mr. Romney's foreign investments. Democrats fling around words like "tax haven," "offshore account" and "secretive investments." But according to their annual financial disclosures, a number of West Wing staffers are wealthy and have foreign holdings.
They have bonds from around the globe. Through international mutual funds, they own stock in holding companies in tax havens like the Caymans, Bermuda, Guernsey, Curacao and the Isle of Man.
There's nothing wrong with any of this. But if Mr. Obama excoriates Mr. Romney for foreign investments, then why doesn't he cleanse his own West Wing staff of millionaire foreign investors?
Have the president's attacks worked? When the Obama campaign launched its Bain attack on May 15, the race was tied at 45% in Gallup's tracking. As of Tuesday, Gallup had it virtually unchanged: Mr. Obama 47%, Mr. Romney 45%.

Still, they have had an effect. The Romney campaign's response—which included whiny demands that the president apologize for his attacks—has unsettled GOP activists, causing them to wonder how prepared Mr. Romney and his team are for the mudfest they've entered. The attacks have drawn attention to the Obama campaign's demands that Mr. Romney release more years of tax returns. And they've allowed Mr. Obama to avoid talking about the continually bad economic news—the lousy June jobs numbers, last Friday's drop in consumer confidence, Tuesday's drop in retail sales and more.

The danger for Mr. Romney is that if these charges go unrefuted, they could discourage swing voters from going for him this fall when they decide whom to support. Therefore, Mr. Romney should challenge Mr. Obama directly—as he did effectively on Tuesday and Wednesday—but in a way that makes the Republican bigger and more presidential than the incumbent.
This is his opportunity to remind voters—in a tone of disappointment and regret, not anger and malice—that Mr. Obama's negative attacks will not put anyone back to work, reduce our growing national debt, or get America moving in the right direction. The attacks are more than just "misleading, unfair and untrue." They are proof Mr. Obama isn't up to the job and no longer worthy of the nation's confidence