Between the 20s and the 60s, the Soviet Union famously politicized genetics, when Trofim Lysenko gained effective control over the argonomic sciences in the USSR. Since Lysenko rejected Mendelian genetics and was generally a complete fraud, but enjoyed the confidence of Stalin, this did incredible damage to the field in Russia.
What if something similar happened in physics? I've seen a few references to Communists describing quantum mechanics as "bourgeois". What if some similar figure, let's say in the early 30s, gained the confidence of Stalin arguing against the new field of nuclear physics, similar to the Deutsche Physik movement in Germany.
Of course, once the A-bomb - or even just the Manhattan Project - proves that there's something to this fission business after all, I'm sure Stalin would change course pretty quickly. But how much damage could be done in the meantime? Might the Soviet atomic bomb be delayed, or would their Manhattan Project intelligence be enough to make up for the damage?