JFK explains very well the relationship between tax policy, tax revenue, employment and prosperity in this video from 1962. JFK was right -- when taxes are too high, it retards both economic growth AND tax revenues to the government. Sometimes, cutting taxes to a more optimum level results in rising prosperity AND rising tax revenues. It's amazing how few liberals understand this basic economic truth.
JFK's 1962 tax policy is much closer to what Romney wants than what Obama wants, fifty years later. At the VP debate, Ryan mentioned this to Biden, and Biden contemptuously asked, "So now you're Jack Kennedy?" Ryan responded, "I'm closer to him than you are." Ryan was right.