Behind the circus atmosphere of this year’s election stand two competing sets of economic proposals that would have very different — and serious — effects on the nation and the world. The Republican nominee, Donald J. Trump, has proposed major tax cuts that observers say would incentivize work, but force hard choices of deep cuts in government spending or a ballooning deficit. He has floated the idea of imposing steep tariffs on goods from China and Mexico, and proposed major limits to immigration. The Democratic nominee, Hillary Clinton, goes in the other direction, proposing raising revenue largely through taxing the very wealthy, and offering an array of tax relief proposals for the middle class. The candidates will compete for the hearts and minds of an electorate that has seen an economy that has recovered from the Great Recession, but has been transformed in structure, from old-style manufacturing to high-tech industry and services.…