In 1770, British troops sent to enforce London’s colonial policy of taxation without representation had already been occupying Boston for two years and were confronting hostility from the locals. An angry crowd began throwing rocks and snowballs on March 5, and the British troops opened fire. After the soldiers, under the command of Capt. Thomas Preston, stopped shooting, the eventual death count of civilians would reach five — and the Boston Massacre entered American history.

When a furious Massachusetts government indicted Preston and his soldiers for murder, Boston lawyers, certain that defending such despised clients would kill their careers and permanently alienate their neighbors, refused to represent the defendants. But one man, John Adams, an open critic of the British occupation, believing that a just legal system depended on a fair trial for the accused and able counsel defending them, risked his professional and political future as well as his personal safety by defending the British soldiers.

Of his courageous act, Adams would later write that defending Preston and the others was “one of the most gallant, generous, manly and disinterested actions of my whole life and one of the best pieces of service I ever rendered my country.”

Some 237 years later, in the second presidential term of George W. Bush, Charles Stimson, the deputy assistant secretary of defense, called it “shocking” that leading U.S. law firms had represented, free of charge, detainees held at Guantanamo Bay. He publicly argued that these law firms would be penalized financially when their corporate clients found out to whom they were providing counsel.

In a radio interview, Stimson said: “I think, quite honestly, when corporate CEOs see that those firms are representing the very terrorists who hit their bottom line back in 2001, those CEOs are going to make those law firms choose between representing terrorists or representing reputable firms.”

He then read out a list of the law firms whose attorneys had represented detainees. His open antagonism to the principle of a defendant’s right to representation and his unsubtle threat to defense counsel led to editorial condemnation and the loss of his job.

But now it’s mostly political liberals, not conservatives, who are attacking a highly respected American lawyer for “defending the indefensible,” which in this case is not any accused criminal, but a federal statute passed by both the U.S. House and Senate and signed into law by President Bill Clinton — the Defense of Marriage Act, which defines marriage as a legal union between one man and one woman.

The Obama administration had announced that the Department of Justice would not defend the constitutionality of DOMA against court challenges, but the Republican-controlled House of Representatives hired former U.S. Solicitor General Paul Clement, then of King & Spalding, a major national firm, to defend the law.

At which point, the Human Rights Campaign, the country’s pre-eminent gay rights political and legal organization — boasting that it had contacted many of King & Spalding’s most prominent clients and enlisted lesbian, gay, bisexual and transgender student groups at leading law schools to criticize the decision to represent — launched an all-out high-pressure offensive against the law firm. King & Spalding folded like a tent in a hurricane or a five-dollar suitcase.

To his credit, Clement quit the firm and will continue as counsel to the House. The Human Rights Campaign did the political equivalent of an end-zone victory dance.

Forgotten by too many of my fellow liberals in this fracas is that by pressuring able, experienced lawyers to refuse to defend an unpopular side means inevitably that the representation will be done by the less able and inexperienced.

Our legal system urgently needs committed, effective advocacy on both sides. To his credit, Attorney General Eric Holder did not duck the issue: “Paul Clement’s a great lawyer. He’s done a lot of great things for this nation.” By agreeing to take this unpopular case, “I think he was doing that which lawyers do when we are at our best.”

Just like John Adams.

Mark Shields is one of the most widely recognized political commentators in the United States. The former Washington Post editorial columnist appears regularly on CNN, on public television and on radio. Click here to contact him.