Unless you happen to be a multi-millionaire living only for today and with your money carefully hidden off-shore, understanding the "national" interest is easy; it is the same as yours.
Workers are disillusioned and giving up, while the stock market is booming, and income disparity was at historic heights even back in 2007 when the anti-regulatory Republicans were mumbling nonsense about the tide that “lifts all boats.” Over the last five years we have all seen what has happened to the boats of virtually everyone. The socio-economic foundation of American democracy is cracked and crumbling.
The story of the post-Reagan era up to 2007 is given in the astounding chart to the right (made by Mother Jones but using Congressional Budget Office data) showing how the "Reagan Revolution" totally ignored the bottom 80% (!) of Americans and passed a few crumbs to the next 19% in order to enrich the top 1%. As for the story of what has happened since 2007 (with the Democrats now fully engaged in running the bipartisan financial system by the rich, of the rich, and for the rich):
At 63.6%, the portion of the working-age population participating in the job market is now at its . [CNN
A choice does exist, though few Americans being impoverished by this bipartisan government of, by, and for the rich, seem awake enough to consider how their votes relate to their financial tribulations.
The choice is to recognize the control of the super-rich over the two-party system and walk away by voting for independent parties. Consider, for example, the specificity of this comment by Jill Stein, candidate for Green Party nomination:
The Green New Deal will end unemployment in America. Of course, such a thing as ending unemployment would never occur to Washington politicians because their corporate backers depend on the threat of unemployment to keep wages down. But ending unemployment, and more, is front and center on the minds of Greens.
As Greens we are committed to improving the conditions of working people by an immediate halt to home foreclosures and evictions, and guarantying health care for everyone as a human right through Medicare for All.