Sanders will be unable to do anything that he wants if Congress stays as a republican majority.
Sanders' economic ideas themselves are also unsound. The way he thinks he can do everything is basically create these massive welfare, healthcare, and college loan reform initiatives and just take the money away from the rich to pay for them.
You don't take (too much) money away from the bloody rich. What stops them from moving the HQ out of the US and just moving? You can't take their green, or it won't trickle down. Same thing for raising minimum wage - people will HAVE to get fired and human work will be too expensive that people will just start looking at automation for making your hamburger. You can't raise the prices of fast food and expect profits to go up - people don't want to pay 58 bucks for a Big Mac. This is simple economics.