As President Barack Obama plays an agonized Hamlet over Afghanistan, the ice is cracking beneath his feet on Capitol Hill. In the House, but especially in the Senate, major figures are already distancing themselves from any commitment he may make to boost U.S. troop levels in Afghanistan—even before he makes it. On Tuesday, the congressional leadership trouped to the White House for a briefing and pep talk on the president’s Afghanistan policy. Senate Majority Leader Harry Reid of Nevada declared afterward, “There was a general discussion there. I hope people aren't talking in the abstract saying, ‘Whatever decision you make we'll support.’ That came from the minority.” He added that Obama “didn't lay out a strategy.” This was an “abstract” endorsement, if it was that. Already under fire for a stimulus package that has run out of steam and a health-care reform plan that was shaped in Congress and not in the executive branch, Obama is discovering that it is the figures of greatest stature in his own party on international affairs who are signaling their hesitance to follow him unconditionally into the high mountain passes of Afghanistan.

Sen. Carl Levin of Michigan, veteran chairman of the Senate Armed Services Committee, this year celebrated his 30th anniversary in the Senate and is serving his sixth term. So when Levin chose CBS’ Face the Nation last Sunday to voice his opposition to approving a new troop surge to Afghanistan, it did not go unnoticed. “I would not commit to more combat troops at this time. There are a lot of other things that need to be done to show resolve. What we need a surge of is Afghan troops,” Levin said. “When I was in Helmand Province just a month ago, we were told by the local folks what they want is their Afghan army to be strengthened. And the ratio of Marines to Afghan soldiers when we were down in Helmand Province was five Marines for one Afghan soldier. That is exactly the wrong ratio. It ought to be reversed from that.”

It is virtually unprecedented for leading Democratic barons to signal their refusal to approve a commitment of U.S. forces overseas by their commander-in-chief—before he even asked for it.

The leading figure of the Democratic Party in the Senate on military issues, with a quarter-century more national experience in national politics than the sitting president, was flat-out breaking ranks with his commander-in-chief on an issue of war and peace without even waiting for Obama to make up his mind first.

Rep. John Murtha of Pennsylvania went Levin one better. On Sept. 14, Murtha, chairman of the House Defense Appropriations Subcommittee, uttered the taboo “V” word, comparing the new surge Gen. Stanley McChrystal is seeking to the dispatch of the half-million troops Gen. William Westmoreland demanded in Vietnam 44 years ago.

“In Vietnam it took 500,000 troops and that didn't solve the problem. So we have to take a different approach," Murtha told Foreign Policy magazine in an interview. "I think that's what [Gen. McChrystal] is trying to do."

"Look how long it took us to get 22,000 more troops, it took 18 months! Jesus Christ!" Murtha said. "When they talk about more troops they act as if you can send them in immediately."

• Peter Beinart: Bury the Vietnam AnalogyLevin and Murtha are of central importance because in the overwhelmingly domestic-policy-oriented and war-averse Democratic Party of the past 37 years—a pattern dating back to the 1972 presidential candidacy of Sen. George McGovern—only a handful of the party’s members have had the nerve and the desire to immerse themselves in military issues. Their reward from their party colleagues has been to serve as the wise men (they are almost never women, except for former Sen. Hillary Clinton) to whom almost all of their colleagues defer without question. Such figures almost always serve as party loyalists, rallying the faithful to support presidents Jimmy Carter and Bill Clinton on their national security policies. It is virtually unprecedented for leading Democratic barons to signal their refusal to approve a commitment of U.S. forces overseas by their commander-in-chief—before he even asked for it.

Levin and Murtha may be far more outspoken than many of their colleagues, but the unease is widespread.

Perhaps the most important figure in the Senate to declare that he is already “rethinking” U.S. policy on Afghanistan is Sen. John Kerry. He was, after all, the Democratic presidential candidate in 2004; notwithstanding the distortions of partisan media, his personal combat record in Vietnam was heroic. Kerry became an outspoken and principled opponent of the war in Vietnam while it was still raging. There would be nothing more devastating to Obama’s credibility as a war leader than to face major criticism from such a quarter.

At least five other Democratic senators—Dianne Feinstein, Barbara Boxer, Robert Casey, Sherrod Brown, and Bernie Sanders—are all “rethinking” their positions on Afghanistan, too. And Speaker of the House Nancy Pelosi, arguably the strongest and most effective leader the Democrats have had in the House since “Uncle Sam” Rayburn, is telling people that support for a strengthened U.S. ground presence in Afghanistan beyond the next year or so may not be there.

The willingness of Obama and his tough-talking but remarkably toothless Chief of Staff Rahm Emanuel to outsource legislative powers on every major issue of the day has been well-documented and commented upon by pundits across the political spectrum. But at least those crucial pieces of legislation—the economic recovery, health-care reform—were outsourced within the Democratic Party on Capitol Hill. Now Obama has created a vacuum in which it appears he has outsourced the highest level of military decision-making—not even to his secretary of Defense, but straight to down to a ground-forces commander, whom his National Security Adviser Jim Jones and Secretary of Defense Robert Gates felt compelled to slap down for near-insubordination.

Historical memories are always short in modern American politics. In his approach to Gen. McChrystal, Obama is apparently unaware that another Democratic president, Harry Truman, effectively sacrificed any hope of re-election in 1952 in order to deny Gen. Douglas MacArthur the chance to usurp the responsibility of the president of the United States to make up his own mind on the most important decisions of war and peace. Some 11 years after Truman fired MacArthur in 1951, the wisdom of maintaining that precedent was confirmed when President John F. Kennedy successfully withstood the pressures for escalation from Gen. Curtis LeMay and his fellow super-hawks during the Cuban Missile Crisis.

Lyndon Johnson at least could still count on strong support from his own party for the now-infamous Gulf of Tonkin Resolution in 1964. Johnson was still riding the wave of sympathy generated by the assassination of John F. Kennedy at the time. And when he approved the flooding of South Vietnam with half a million U.S. troops the following year, he was still the colossus of U.S. national politics, having won the greatest electoral victory in history over Barry Goldwater the previous November. And no one doubted Johnson’s decisiveness or leadership capabilities on the home front. He had just pushed through the greatest wave of liberal reforming legislation in the 30 years since Franklin Roosevelt’s second New Deal of spring 1935.

Before them, yet another Democratic president, Woodrow Wilson, was the first effective liberal reforming Democrat in modern American history until the U.S. was drawn into World War I. A week before the Armistice was signed in November 1918, Wilson lost control of both houses of Congress and his great liberal reforming drive was stopped dead in its tracks. Then he lost the peace to Republicans desperate to frustrate him and seize the presidency back for themselves. It took 15 years and the full horrors of the Great Depression to get the next one going again. Congressional Democrats are nervous over Afghanistan for a very good reason.

Martin Sieff is chief global analyst for The Globalist. He was previously chief news analyst, managing editor for international affairs and defense industry editor for United Press International, and Soviet affairs and State Department correspondent for The Washington Times. He is the author of Shifting Superpowers: The New and Emerging Relationship between the United States, China and India (Cato, January 2010) and Cycles of Change: The Patterns of American Politics from Thomas Jefferson to Barack Obama.