If one wants to look for the moment where Mr. Obama’s campaign started to go sour, mark the point where he veered onto the protectionist path — and left it so that the presidential candidate in the race who is going to be defending one of the landmark policy achievements of the Clinton-Gore administration is going to be, unless Mayor Bloomberg gets in, none other than the Republican, Senator McCain. The achievement of which we speak is the North American Free Trade Agreement, and in the past few days, Senator Obama has been launching increasingly shrill attacks on it.

The Wall Street Journal reported yesterday that Mr. Obama has distributed fliers in Ohio showing “a locked factory gate with a large ‘closed’ sign on it” and language blaming Senator Clinton for having backed Nafta. In his speech Tuesday night in Houston after winning the Wisconsin primary, Mr. Obama said, “We’re here because there are workers in Youngstown, Ohio, who’ve watched job after job after job disappear because of bad trade deals like Nafta, who’ve worked in factories — who’ve worked in factories for 20 years, and then one day they come in and literally see the equipment unbolted from the floor and sent to China.”

Mrs. Clinton, rather than defend the value of free trade to growing our economy by expanding American exports, providing cheaper goods for American consumers, and increasing overall prosperity both at home and abroad, has been scrambling away from one of her husband’s greatest accomplishments. The Journal article reports that the Clinton campaign responded to the Obama flier by saying that, contrary to its claim, the candidate never said that Nafta was a “boon” to the American economy. Tuesday, Mrs. Clinton herself, campaigning in Ohio, said, “My opponent has taken to attacking me on Nafta. The fact is, neither of us were in the Senate at the time, and I’ve long been a critic of the shortcomings of Nafta.” Mrs. Clinton may not have been in the Senate at the time, but she was in the White House at the time, and she wants credit for that as part of her 35 years of experience that is supposed to make her qualified to be president. Breathtaking.

So who is left to defend the trade agreement that President Clinton and Vice President Gore worked so hard to achieve? Well, one can just click on YouTube to bring up a video with Mr. McCain explaining, “I know Nafta was a good idea. It’s created millions of jobs, and it has helped the economies of all three of these nations. All you have to do is go to Detroit and see the thousands of trucks lined up every day, or go to our Southern border. …Free trade is something I think that is vital to the future of America. As a free trader, I will open up every market in the world.”

Mr. McCain went on to acknowledge the need to assist displaced workers and to make the point that while some jobs would be lost because of trade, overall, jobs would be gained. It is the sort of intelligent answer that Mr. Clinton might have given in 1996 or Mr. Gore in 2000. What a shame that no one from their party is conveying that message in our current campaign season, and that the party that brought us Nafta in the 1990s is in its current iteration resorting instead to fear-mongering and protectionism. It’s hard to see which is more amazing — that this would come from Mrs. Clinton, whose husband signed Nafta into law, or that it would come from Mr. Obama, who is campaigning as a uniter while cynically telling American workers that job growth in China and Mexico comes at their expense, or that the person left to carry on this part of the Clinton legacy is the Republican.