Whatever their differences, the Iraq and Vietnam wars have in common congressional efforts to end them.

Despite protests, both conflicts were escalated in hopes of bringing them to some sort of satisfactory conclusion. The current Bush surge has added some 25,000 troops to the U.S. force of about 140,000 in Iraq. President Johnson in 1968 faced a request from his top general in Vietnam for 206,000 troops in addition to the 485,600 already there.

But the two presidents responded differently to objections by the public, Congress and some top military leaders. Mr. Bush pushed ahead with the escalation. Mr. Johnson called in senior advisers (known as the Wise Men) and got such a bleak appraisal of the prospects that he decided to quit the presidency.

In both wars, congressional opposition was slow to develop. In the Iraq war, serious congressional demands for an exit timetable began only after the Democrats took control of both houses this year. For a long time, Wayne Morse, D-Ore., and Ernest Gruening, D-Alaska, cast the only Senate anti-war votes over Vietnam. Later, more Democrats and some Republicans joined the opposition, and William Fulbright, D-Ark., galvanized the nation with televised public hearings attacking the war policy.

Congressional tactics varied as well. In the Iraq war, only a few Republican senators have joined the opposition; toward the end of the Vietnam War, Congress repeatedly withheld funds for expansion and eventually even halted the bombing campaign as President Nixon withdrew U.S. troops and “Vietnamized” the war.

Both of these long wars stretched U.S. military manpower thin and raised questions of why the United States should be involved at all. In the Iraq war, the original justification that Saddam threatened the use of weapons of mass destruction and had something to do with the 2001 terrorist attacks soon evaporated. The United States has found itself involved in an Iraqi civil war, even though President Bush continues to describe it as part of a war on terror.

In the Vietnam War, the end came as a humiliating defeat as helicopters rescued the last of the Americans and some Vietnamese collaborators from a rooftop. But, after a rocky start, a united Vietnam has seemed more capitalist than communist and has become a friendly trading partner of the United States.

Iraq’s future, with or without a U.S. presence, defies prediction.