Even if Sanders wins, the US is not going to become socialist overnight (thank goodness...). The Senate, Supreme Court, and (periodically) the House will block basically every little thing he does. If he plays his cards right, he might be able to push through one or two major things, but it won't be exactly what he wants, and it's not going to completely reshape US politics.
The presidency is more of a figurehead than administrative position IMO. There's no way for 1 person to effectively govern 300,000,000. The ability of one president to have a broadly transformative effect on the entire country just isn't something that happens. There's too many machinations at work to allow a single person to upset the power structure... I think Obama was a good example of this. Much like with Trump, people thought Obama becoming president was going to destroy the country. Instead, he largely produced more of the same.
Sanders being elected would definitely represent a shift in attitude that is reactive of Trump, but I agree that ultimately he'll have to put any grand ideals on hold and compromise down to the status quo, just like every other president of the last 30 years.