On 23 October 1983, a truck-bomb rammed into a barracks close to Beirut airport, killing 241 US Marines participating in a multinational force sent to keep the peace between the murderous factions of Lebanon. It was, writes the then Secretary of State George Shultz in his recently published memoirs, the 'worst single disaster of the Reagan administration'.
Within 48 hours, US troops had landed in Grenada, ostensibly to rescue American students, in fact to prevent the installation of a pro-Cuban regime on the Caribbean island. The operation was 'a shot heard by usurpers and despots of every ideology', claims Mr Shultz.
The Bosnian crisis, in terms of both complexity and unappealing choices, has few rivals in modern times. But as the White House inches towards direct military involvement, analogies are being aired on every side. The starkest underscore the fundamental moral dilemma that has divided the administration and Congress. To do nothing, say proponents of force, would sanction an 'ethnic cleansing' not witnessed in Europe since the Nazis sought to exterminate the Jews. Those urging caution point to a scarcely less traumatic lesson of history: ill-considered intervention, miring Washington in another Vietnam.
Hence the conflicting pressures on Mr Clinton, and the growing clamour within Congress that any military action be put to a vote, and that the President - who after the Bosnian Serbs' de facto rejection of the Vance-Owen plan seemed yesterday to be nearing the end of his patience - make a national address to a sceptical country to explain why the crisis can wait no longer, and why US interests are directly at stake.
Everyone wishes Bosnia were as straightfoward as Grenada, or as relatively low risk as the US-led humanitarian mission to Somalia which formally ended this week: 'You have proved that our involvement in multilateral efforts need not be open-ended or ill-defined,' said Mr Clinton in a welcome-home ceremony for the Somalia troops at the White House.
But everyone knows that in Bosnia such conditions will be desperately hard to meet. Behind repeated promises of bipartisan backing for whatever the President decides, the divisions on Capitol Hill cut across every traditional battleline. Democratic liberals who only two years ago were opposing the Gulf war are among those most passionately urging action now.
Normally a Republican military hero would be expected to agree. But Senator John McCain of Arizona, a former US Navy pilot shot down and imprisoned for more than five years in Vietnam, is leading the faction that insists the US must stay out, warning against the siren appeal of a 'feel-good' policy whose consequences have not been thought through.
In September 1983, Mr McCain was a new Congressman who warned of the perils of having sent the Marines to Beirut. To many today, that tragedy seems the closest of all the imperfect historical parallels to Bosnia, a snakepit of ancient factional hatreds where US forces, even under a UN umbrella, would again be the symbolic enemy par excellence.