On Wednesday Donald Trump demanded that Congress move quickly to enact his tax reform plan. But so far he has not, in fact, offered any such plan. Not only is there no detailed legislative proposal, his administration hasn’t even settled on the basic outlines of what it wants.

Meanwhile, 17 Senate Democrats — more than a third of the caucus — have signed on to Bernie Sanders’s call for expanding Medicare to cover the whole population. So far, however, Sanders hasn’t produced either an estimate of how much that would cost or a specific proposal about how to pay for it.

I don’t mean to suggest that these cases are comparable: The distinctive Trumpian mix of ignorance and fraudulence has no counterpart among Democrats. Still, both stories raise the question of how much, if at all, policy clarity matters for politicians’ ability to win elections and, maybe more important, to govern.

About elections: The fact that Trump is in the White House suggests that politicians can get away with telling voters just about anything that sounds good. After all, Trump promised to cut taxes, protect Social Security and Medicare from cuts, provide health insurance to all Americans and pay off the national debt, and he paid no price for the obvious inconsistency of these promises.