I wouldn't underestimate the message a Bernie presidency would send. The winds of change would be blowing. A president alone can't do shit without Senate and Congress following along. A Bernie presidency would send the message that the majority of people is ready for systemic change and a systemic change can get dangerous to those rich folk. Also they can't directly veto stuff since they pull the strings through donations and powerplays in the background. His first step would be to tax the wealthy and hopefully curbstomp Wall Street as well as balancing the budget. We are currently heading straight to another financial collapse and this time it might affect the real economy on a much grander scale than 2007. Actually it might be good to keep Trump for a bit longer so he can be the face of the crisis.
Bernie being president would be a pretty clear message BUT that won't change a simple fact: Bernie will have virtually no allies in the senate and congress. Bernie's policy positions are well more popular than he is given credit for when it comes to congress and senate members they are almost violently unpopular. And this is largely because pretty much the entirety of congress and the senate is inherently, comically, corrupt in this regard. bernie would be basically proposing tax hikes to:
1.- people who will specifically pay more taxes.
2.- People who take campaign donations from people whose only interest is to see their taxes stay the same or lowered.
The above applies largely to both parties.
Another bit worth considering is what policies tend to get bipartisan support nowadays. Generally its 3 things (though there can be more depending on the circumstances): The first would be tax cuts, the second would be spying on people and the third would be increasing military budgets. Bernie opposes basically all 3 of those... Meaning he will almost invariably get bipartisan opposition on them.
Climate change wise.... democrats are technically for regulation in this regard BUT mainstream democrats are usually extremely weak on this sort of thing. Over concerns of what it will do to the economy (and their donors).
A bernie presidency would be rocky, filled with a crapton of infighting within bernie's own "allies" and the odds of him getting something done are low at best. The only upside IMO is that there will be at least a chance for meaningful change... contrary to joe "nothing will change" biden (who is still better than trump though).
There is also bernie's main policy position... remove money out of politics. Being president won't actually give him the power to actually solve this issue. This issue is solved via a constitutional amendment... Being president would give bernie an unparalleled chance to get the message out on this but it won't actually give him the power to simply pass legislation on this. Add to that, the congress and senate members who basically profit from this would be the ones to have to vote in favor of bernie's amendment.
It'd be a wild ride but under any reasonable scenario a bernie presidency would have literally everything stacked against it.