THE OBAMA administration has gotten some grim signals this week in response to its effort to “change the calculation” of Syrian ruler Bashar al-Assad. In an interview broadcast Thursday, Mr. Assad said there had been “a shift in the balance of power” in the country’s civil war “in favor of the armed forces” and that he had “absolute confidence in our victory.” He brushed off suggestions that he step down in favor of a transitional government and said he wouldn’t hesitate to nominate himself for a new term when his presidential mandate ends in 2014.

Clearly, the strategy that Secretary of State John F. Kerry announced in February has failed. The idea was that the United States would, by providing additional support to the opposition, persuade the Assad clique that its cause was lost, opening the way to a negotiated process in which Mr. Assad would yield power. But Mr. Assad doesn’t believe he is losing — and he is not wrong in claiming that his fortunes have risen in the past several months. As The Post’s Karen DeYoung and Joby Warrick reported Thursday, Russia has continued to supply his army with weapons , while thousands of fighters of the Lebanese Hezbollah militia have joined the war on his side. The regime appears close to retaking the strategic town of Qusair, which lies along a supply route from Lebanon, and has made gains in the Damascus area.

Meanwhile, the United States has yet to provide the rebels with the lethal aid it was said to be considering months ago. Nor has it taken any other substantial steps to strengthen them. Instead it has chosen to go along with a Russian proposal to convene another peace conference in Geneva. Mr. Assad and his backers in Moscow intend to use the talks to restore the regime’s legitimacy and buy time for the deployment of advanced Russian weapons systems to deter outside intervention.

The opposition, for its part, is balking at participation. That’s understandable, because there is no prospect that the conference will lead to Mr. Assad’s departure. What’s harder to understand is why Mr. Kerry continues to vigorously pursue the conference, having failed to accomplish the necessary predicate of changing the balance of power on the ground. Unfortunately, the most plausible answer is that the administration has allowed itself to be played by Russian President Vladi­mir Putin, who is seeking to restore Moscow’s influence in the Middle East by thwarting the U.S. goal of regime change in Syria. Not for the first time, President Obama and his aides appear to have bet that Mr. Putin would turn on Mr. Assad and help force him from power. In doing so, they have fundamentally misread the Russian ruler and his intentions.

As we have written previously, the only hope for an acceptable political settlement in Syria lies in an intervention that would decisively shift the balance of Syria’s war — through arms supplies to the rebels and airstrikes to eliminate the regime’s air power. If Mr. Obama is unwilling to take such steps, he ought also to eschew diplomacy that makes his administration appear foolish as well as weak.