Barely a fortnight ago, the mood here was vastly more assured. Certainly, the President led his Communist opponent Gennady Zyuganov by just three points, but the speed with which he co-opted Mr Lebed and evicted several hardliners from the Kremlin inner circle convinced the Clinton administration that the candidate which it had supported from the outset had wrapped matters up and Russia's "democratic" future was assured.
Since then, however, that rosy scenario has unravelled. Mr Lebed has put an authoritarian and anti-Semitic streak on ugly display, and the White House has had to watch in embarrassed silence as Mr Yeltsin disappeared for days with what was, officially, "a cold".
Visually, the recent authorised images of a slow, stiff- spoken Boris Yeltsin are reminiscent of nothing so much as the Soviet Union of the early 1980s, when a procession of geriatric leaders - Brezhnev, Andropov, Chernenko - made brief, minutely-choreographed appearances that raised more questions than they answered. But, however flawed and secretive, the Soviet system was at least broadly predictable. Not so the erratic and capricious Yeltsin regime.
Even a fit Mr Yeltsin would face mountainous economic problems. His campaign handouts have driven the budget deficit far beyond the targets laid down by the IMF as conditions of this spring's $10bn loan, pushed through largely at US insistence. At the least, economists warn, the consequence will be a new surge in inflation: at worst, a full-blown financial crisis that will scare off Western investment and reinforce anti-market, authoritarian attitudes in the country.
As it is, his health seems more fragile than ever, creating uncertainty over where day-to-day power lies and (assuming he wins) offering still more leeway for Mr Lebed, a figure viewed with growing nervousness and distaste by the US.
One consolation for US policy-makers is Mr Lebed's opposition to the Chechen war, and his readiness to make real concessions to obtain a genuine end to the fighting. But they doubt even a law-and-order hawk like Mr Lebed can control crime and break the power of the Mafia groups who have thrived under Mr Yeltsin.
Mr Lebed is seen as a de facto Vice-President, whose ambition for the top job makes it more than likely the two men, both domineering and instinctively authoritarian, will clash. The Lebed/Yeltsin tandem, in other words, is a recipe for instability.
That likelihood, added to growing nationalism and xenophobia across the political spectrum, can only dim prospects for final ratification of arms control treaties. Washington may also find itself under great pressure to press ahead with Nato enlargement far more quickly than it would like.