Keynesian economics worked very well for this country for many years. Then came the "Reagan revolution", and the Republicans replaced it with supply-side "trickle-down" economics. That turned out to be a disaster. It depressed wages for most American workers, shrank the middle class, created the biggest gap in wealth and income this country has seen since before the Great Depression, cost the country millions of jobs, created a huge budget deficit, and set up the economic conditions that threw this nation into the Great Recession.
Amazingly, Paul Ryan and his Republican cohorts now want to continue that failed policy -- inspite of the damage it has already caused. It just shows that they don't really care about the economic viability of this country. They just want to make sure the rich (their real constituency) keep getting richer, so they can keep filling their own campaign chests. They need to learn that political ideology should never trump economic reality -- and what's best for the vast majority of Americans.