Senator Ben Cardin, (D-MD), added his voice to those questioning Chuck Hagel's fitness for the job as defense secretary, faulting his former Senate colleague's preference for U.N. sanctions against Iran over U.S. bilateral measures.

Interviewed on MSNBC on Tuesday, Cardin took issue with Hagel's contention that it is wiser to pursue U.N. sanctions to compel Iran to curtail its nuclear ambitions than to impose unilateral U.S. sanctions.

"I have not supported unilateral sanctions because, when it is us alone, they don't work and they just isolate the United States," Hagel told his hometown paper, The Journal Star on Monday. "United Nations sanctions are working."

Cardin countered that the United States is "looked upon internationally as the leader and we have a responsibility to lead on sanctions." In a sense, Cardin and Hagel are both partly right. U.N. sanctions are having an impact on Iran's ability to do business. But they would not have nearly the same sting if they were not reinforced by a patchwork of U.S. and European measures that target Tehran's financial system and oil industry.

But Cardin used a curious example to make his case. In his interview, Cardin claimed that U.S. leadership on sanctions against South Africa in the era of white rule had helped bring about an end to Apartheid.

"If the United States would  waited for the international community we dare say ... [it] ... would have been a lot longer before it ended its Apartheid state," Cardin said. "The United States showed leadership, the rest of the world followed."

Not so fast, Mr. Senator. The U.S. position on sanctions varied since 1948, when South Africa's nationalist party came to power adopting a raft of laws that codified the country's apartheid system that relegated the country's black to second class citizens. But it could hardly be viewed as leading the cause.

The first stirring of unease about South Africa's discriminatory policies emerged in 1946, even before the nationalists came into office, when India asked that the country's discrimination of ethnic Indians be placed on the agenda for discussion during the first session of the U.N. General Assembly.

The U.S. position dating back to the 1960s could be best described as highly ambivalent -- if not outright hostile to sanctions. Washington backed a 1960 Security Council resolution deploring the South African police's killing of 69 unarmed protesters in Sharpesville. And the John F. Kennedy administration backed a voluntary arms embargo. But U.S. administrations dating back to the 1960s opposed calls by developing nations, including African governments, for a mandatory arms embargo and economic sanctions.

In October 1962, a senior U.S. diplomat at the U.N., Francis Plimpton, vowed to "continue to oppose" the imposition of U.N. sanctions on South Africa, dismissing them as ineffective, according to a useful chronology published by The Peterson Institute for International Economics.

On August 7, 1963, the United States voted in favor of a U.N. Security Council resolution recommending states cease the shipment of arms to South Africa, and Washington decided to end U.S. military sales. But days before the vote, Adlai Stevenson, then U.S. ambassador to the United Nations, argued against making them mandatory. "The application of sanctions in this situation is not likely to bring about the practical result that we seek," Stevenson said at the time. "Punitive measures would only provoke intransigence and harden the existing situation..."

It would be another 14 years -- in response to the violent repression that followed the Soweto riots -- until the United States under President Jimmy Carter backed a mandatory arms embargo against South Africa. The U.S. cut off exports of any items to South Africa as there was reason to believe it would be used by the military. But the United States and its European allies still resisted U.N. General Assembly calls for an oil embargo on South Africa.

U.S. opposition to sanctions resurfaced following President Ronald Reagan's presidential election. Reagan's assistant secretary of state, Chester "Chet" Crocker, inaugurated the policy of "constructive engagement" with the apartheid regime, relaxing trade restrictions on the South African military. But as the Reagan administration sought to bolster relations with the South African government, civil society groups in the United States and abroad began to mobilize economic and political pressure on the Pretoria. "The international economic actions against South Africa that were most damaging were taken by private actors, not governments," Philip Levy argued in this 1999 paper.

As for Iran, Cardin said he still needs to understand why Hagel would be willing to forgo the imposition of unilateral sanctions on Iran when the international community could be expected to follow our lead if we did. "These are questions I think as a senator I have a responsibility to get his answer before making a decision on whether to support his confirmations," he said.

Fair enough. But the assumption that the world will follow is far from proven. Russia and China have made it clear they would block any new U.N. sanctions resolutions that targeted Iran's economy. The truth is that it is extremely difficult to fairly assign credit for the success or failures of sanctions in South Africa or Iraq. But it would help to have a reasonably clear-headed account of the facts.

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