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The Wall Street Journal editorial board, an influential conservative outlet, blasted Mitt Romney on Wednesday night, writing in an piece that the Republican candidate was “squandering an historic opportunity” and “is losing ground.”

The blistering unsigned editorial came after Romney’s campaign has struggled this week to explain its position on the Supreme Court’s health care ruling. A top Romney aide on Monday had declared the fine for people who don’t purchase insurance under the law is not a tax, differing from what the the court ruled last week. But then Romney himself contradicted that adviser in an interview Wednesday, saying he did view the penalty as a tax.

Many conservatives have used the court’s ruling to cast Obama as raising taxes on the middle class. (In fact, fewer than 1 percent of Americans are exposed to not purchase health insurance under the law, and face the fine, which is either $695 or 2.5 percent of income, whichever is higher) But Romney has struggled with the issue, since the health care law he passed in Massachusetts fines people who don’t have health insurance in the same way “Obamacare” does.

“This latest mistake is of a piece with the campaign’s insular staff and strategy that are slowly squandering an historic opportunity. Mr. Obama is being hurt by an economic recovery that is weakening for the third time in three years. But Mr. Romney hasn’t been able to take advantage, and if anything he is losing ground,” the editorial says.

Later, the editors write, “Meanwhile, the Obama campaign is assailing Mr. Romney as an out-of-touch rich man, and the rich man obliged by vacationing this week at his lake-side home with a jet-ski cameo. Team Obama is pounding him for Bain Capital, and until a recent ad in Ohio the Romney campaign has been slow to respond.”

(RELATED: See theGrio’s story on Romney’s tax comments and our story on how the health care decision helps Obama, but does not guarantee victory in November.)