THE RUSSIAN government had long vowed some form of retaliation after Congress passed, and President Obama signed, a law that imposed sanctions on officials responsible for the death of Sergei L. Magnitsky, a Russian lawyer who died in prison in 2009. Maybe the Russians would pass a similar law targeting US officials? Maybe they would make economic investment for American companies more difficult? Maybe it was all a bluff? Instead, Russia’s parliament approved a cruel gesture — a ban on the adoption of all Russian children by American parents. On Wednesday, the measure went to the desk of President Vladimir Putin, who did not immediately say he would sign it but has coyly supported it all along.