Donald Trump has been smart enough to realize that a large segment of the Republican base is economically disadvantaged and that Republican policies on trade are a part of their problem. He also understands that entitlement programs like Social Security and Medicare are very popular. The Republican Party has been doing what it can to reduce spending on those programs. Trump's style, and much of his rhetoric is not presidential, but he has capitalized on populist discontent in the GOP base to soundly trounce more conventional Republicans who adhere to the Party line. Trump's tax policies and his healthcare plan are very Republican and very bad for this populist base but these policies are drowned out by his promises to bring jobs back to America and to protect entitlements.
When it comes to trade and entitlements Bernie Sanders sounds a lot like Trump. However, his tax polices and his healthcare proposals are progressive where Trump's are regressive. He may overlook the problems that he would face in implementing his policies, but they appeal to the populist base in the Democratic Party. His ideas are as far to the left in a centrist Democratic Party as Trump's are in the Republican Party which has moved to the extreme right under the assurance that its populist base does not understand their own economic interests. Populists in both parties are disenchanted with a political system that serves corporate interests over their own.
Bernie Sanders may move the Democratic Party away from the center right position that it has been forced into by the need to compete with Republicans for campaign funds. That would be a relatively easy transition. The Republican Party cannot easily make that transition. It would have to give up an ideology that defines their Party.