Conventional wisdom dictates that should Bernie Sanders overcome all electoral hindrances and assume the presidency, much of his agenda would not get through the U.S. Congress. Since Sanders comes from the left wing of the political spectrum, it would be nearly impossible for him to persuade moderate Republicans to vote for his proposals.
Traditionally, presidents shepherd legislation through the Congress by consolidating the votes of members from their own party, then by siphoning off the votes of enough moderates from the opposing party to get legislation passed. This is how Lyndon B. Johnson got Medicare through in 1965, how Ronald Reagan pushed his tax cut proposal through in 1981, and how George H.W. Bush won approval for the the Persian Gulf War Resolution in 1991.
Along these lines, many of Sanders's major proposals would have a near impossible chance of passing without major changes to temporize the legislation. The Republicans are likely to maintain control of the House, and while there is an outside chance they could lose the Senate, the chances are de minimus that the Democrats will hold a 60-vote filibuster-proof majority.