What would it take for the US's purchase of Alaska from Russia in 1867 to never go through? There was some significant opposition to it at the time-"Seward's Folly", and the House of Representatives taking their sweet time to appropriate the money- but could this be expanded sufficiently to stop the sale? Or would changing the political conditions in Russia be more effective?
As a follow-up, if the US didn't buy Alaska, would it be likely to be sold to somone else, or could we have Alaska remain part of the Russian Empire into the 20th century?