Nothing will change federally because there is too much money to be made in politics. Poll after poll shows that US citizens favor legalization. Political talking heads (GOP and Dems both) listen to their donors not their voters because buying TV time is the most effective means to win an election, unfortunately.
I will say that because of Canadian legalization I think this environment is rapidly changing. US companies are beginning to invest heavily in Canadian cannabis. The parent company for Corona just tossed $4 billion into the ring. When big players in the US start throwing that kind of money around, it's only a matter of time before they start spending that money on US politicians. Locally in FL I'm seeing the formation of pro-MJ legalization political action committees. This is unfortunately the first real step towards legalization. The IRS just follows the tax code and they do not have control over the tax code US congress does.
November is coming vote for MJ friendly candidates! We need to have a major shift in the house in order for anything to be done. I think right now with respect to MJ the Senate is close to it's tipping point to be pro-MJ but there are some higher-up talking heads getting in the way. This isn't a red vs blue argument either it's an old vs new argument IMHO.