As U.S.-Russian relations sour, some observers fear the plan to eliminate Syria's chemical arsenal might stall.
This past week, the removal of chemicals from Syria reached the halfway mark. Without pressure from both superpowers, however, some believe Syrian President Bashar al-Assad will begin to drag his feet.
"I think what you're likely to see is that the Assad regime will comply just enough, at a slower pace, as it consolidates its hold over the country militarily," says Andrew Tabler, a Syria expert, at the Washington Institute for Near East Policy.
The plan to eliminate Syria's chemical weapons was hatched at a summit last fall in Geneva. Secretary of State John Kerry and Russian Foreign Minister Sergei Lavrov stood side-by-side and presented an ambitious plan to spirit dangerous chemicals out of the country in a matter of months.
"The United States and Russia are committed to the elimination of Syrian chemical weapons in the soonest and safest manner," Kerry said at the time.
"It's one of the unique instances where both Russia and the United States have come together in a very cooperative way to work on a common goal," says Paul Walker, a chemical weapons expert with the non-profit Green Cross International.
Walker says the Russians were instrumental in getting Assad to go along with the plan. Russia has strong ties with the Syrian regime, and supplies it with considerable military aid to fight its ongoing civil war.
"When the Russians say step up and join the chemical weapons convention, Bashar al-Assad pretty much salutes and says, 'Yes, Sir,'" Walker says.
Syria pledged to remove its most dangerous chemicals by the end of last year, but then it started to stall. Assad said security was the problem, but Western observers suspected he was dragging his feet — drawing out the process to keep America from interfering with the war.
Russia broke the impasse, says Amy Smithson with the Center for Non-Proliferation Studies. In December, it sent dozens of armored trucks to carry the chemicals out of Syria. The trucks addressed Assad's security concerns, but they also sent a message.
"To me that was a very clear signal: Don't drag your feet too much in moving this stuff to port," Smithson says.
Since January, Syria has been stepping up shipments, but as it hits the halfway point, U.S.-Russian relations are reaching a new low. The U.S. condemned Russia's annexation of the Ukrainian region of Crimea, and the two nations traded tit-for-tat sanctions over the past week.
The strain can be seen in the Syrian operation. Under international agreement, the chemicals were to be destroyed aboard a U.S. ship escorted by Russian naval vessels. That escort is off for the time being. If the sanctions get worse, Smithson says that will probably have some type of a ripple effect on how Russia chooses to influence — or not — what Syria does with the remaining shipments.
For its part, Syria probably wants to take its time removing the chemicals, according to Tabler.
"The usefulness of the Assad regime drops off significantly after those chemical weapons are destroyed, because we no longer need the Assad regime to secure their safety," he says.
Without Russian pressure, Tabler expects the shipments to slow while Assad continues his assault on rebels.