MOSCOW — For three years, the power-sharing tandem of Prime Minister Vladimir V. Putin and President Dmitri A. Medvedev purred along like a sports car, quieting skeptics who said that any division of executive authority in Russia would lead to instability. The ambiguous arrangement seemed to soothe tensions, allowing everyone, from pro-Western technocrats to hawkish hard-liners, to believe they were represented at the very top.

But lately the tandem has begun to hiccup and backfire. It is impossible to say whether trust has broken down between the two men, one of whom will increase his power in next spring’s presidential election. But a universe of officials, businessmen and political hangers-on — uncertain whether to show loyalty to one man, the other or both — has “spent the whole last month on the verge of a nervous breakdown,” the economist Vladislav L. Inozemtsev wrote last week in the newspaper Moskovsky Komsomolets.

Mr. Putin invented the arrangement in 2008 when term limits prevented him from seeking the presidency again, and it is largely his choice whether to continue it. He has tried to put a lid on speculation even while working to delay an announcement until the fall on who the presidential candidate will be, but he may be too late.

Winston Churchill compared Kremlin power struggles to bulldogs fighting under a carpet: “An outsider only hears the growling, and when he sees the bones fly out from beneath, it is obvious who won.”