When did the Soviet Union's Politburo essentially stop functioning? (80s, USSR, date)

[Mini-apple-less]

Was Yeltsin pretty much already boss by July 1990 and the 28th Congress when the Communists gave up their monopoly of power, or were the Politburo still pretty much running things behind the scenes until the failed coup in August 1991? I know to a certain extent the Soviet Union was already breaking up in the 80s, but it was really in 1990-91 that things really became dire, to the point of Lithuania going as far as saying they weren't part of the USSR anymore.

[Attrill]

It's hard to put an exact date on it, but Gorbachev's constitutional changes in 1988-89 basically made it toothless. By that point they didn't have the power to throw him out of office, and his changes showed that he saw the institution as being useless in the new scheme of things. Some members of the Politburo did leave it for other posts in the government.

[Mini-apple-less]

I did read that as late as any time in 1990 the Stalinist coup could have been a success (imagine that!) but by 1991 it was essentially too late.