Washington ? On the same evening last week that President Obama went to West Point to outline his plans to send 30,000 more U.S. troops to fight the Taliban and al-Qaida in Afghanistan, the four Massachusetts Democratic candidates hoping to win Ted Kennedy’s Senate seat met in a televised debate.

All four — including the favorite in Tuesday’s primary, state Attorney General Martha Coakley — said they opposed the president’s decision to escalate. Referring to Obama’s promise to begin bringing an unspecified number of the “surge” forces home by July 2011, Coakley said, “It seems to me it’s impractical, given what we think the mission is, the number of troops we’re sending over.

“We really won’t be able to be finished in 18 months and start an exit strategy there,” she said.

The rejection of Obama’s argument by the leading candidate in an overwhelmingly Democratic state shows how much the president has failed to convince his fellow partisans he is right about the biggest national security policy decision of his tenure.

It is symptomatic of a bigger problem; Coakley and her rivals are emblematic of widespread Democratic dissent on Afghanistan.

Listen, for example, to House Speaker Nancy Pelosi, normally the lead voice for pushing Obama’s programs on Capitol Hill. When asked at her Thursday news conference about her pre-speech warning that there was little support for escalation on the Democratic side of the aisle, she reiterated that view, and added that she wanted more briefings on Obama’s rationale and plans before members have to vote on funding for the war.

Carefully avoiding any words that could be interpreted as support for Obama’s policy, she said, “I think we have to handle it with care, listen to what they present and then members will make their decision. Some have already made their decisions, and they have been outspoken on the subject.”

Indeed, many of her closest allies in the House such as Rep. Rosa DeLauro of Connecticut have declared they will oppose paying for Obama’s program. “It will be very difficult for me to support funding for an increased military commitment to fight the Taliban and various insurgent groups that are bringing instability to Afghanistan and Pakistan, particularly when we do not appear to have a credible partner in the Karzai government, and are trying to bring stability to one of the most corrupt countries in the world,” DeLauro said.

That was not the universal reaction. Centrist and conservative Democrats and those who serve on the Armed Services Committee tended to be more supportive of Obama’s decision. Next year, when the additional troops are in the field and the first bills come due, there will probably be enough Democrats willing to join the vast majority of Republicans in funding the Afghan surge.

But the lessons of a previous land war in Asia cannot be forgotten. When Lyndon Johnson escalated in Vietnam, initially both Republicans and Democrats gave him their support — and public opinion was more positive than it is now for Afghanistan.

The defections began on the Democratic left — where the opposition to Obama is most visible today — and by the end, most Democrats and many of the Republicans had abandoned Johnson to his political fate.

A president who wages a war supported mainly by his political foes and opposed by large numbers of his own party is running a huge political risk. Even if he prevails for a time, he pays a price in the loss of his most loyal supporters.

Obama can rightfully claim that he made clear throughout his campaign that he saw a vital need to fight on in Afghanistan. But he has obviously not persuaded many of his important followers as yet that they should endorse his views. And nothing short of success on the battlefield is likely to convince them that he is right.