How much of the 20th century is repealed if the GOP wins in 2016?

[Skill and Chance]

None of it. No one is going to repeal the FDA or EPA, stop being unrealistic. What happened to government after every Republican president since Eisenhower? It GREW.

That was before the Tea Party.

Do you really think the Tea Party would have any affect on the nominating process, or that they even want smaller government? 80% of Republicans thought Bush did a good job while in office. That alone speaks tremendous volumes as to what they actually care about.

The federal government did unambiguously decline as a percent of GDP under Truman (obviously a little something was driving this), Eisenhower, and curiously, Clinton.  It also looks like fed spending/GDP declined under Kennedy and Nixon.  So it's really quite incorrect to claim that government has monotonically grown faster than the economy as a whole like some inherent law of nature.

As for what could change under unified GOP government, I don't think the New Deal will be going anywhere.  After all, the elderly white Republican base depends on its programs more than anyone else.  I would worry more about what SCOTUS could do.  If Ginsburg leaves under a Republican president and senate (the latter basically assured through 2020 in any scenario where a Republican president wins in 2016), Roe v. Wade is gone in 2 years.  If Ginsburg and Kennedy both leave, then no Warren Court precedent is safe.  Expect any civil rights laws that place burdens on employers to be read very, very narrowly.  And the 2020 Dem nominee says thank God for the 24th Amendment...

[Skill and Chance]

Much of the 20th century was terrible, unfathomably horrible events, I wouldn't mind a do-over.

So you'd rather go back to 40 year average lifespans, 2-3% risk of death in childbirth per birth, uncontrolled infectious disease in general, much more violent crime, and slavery/a severe racial caste system being a fundamental feature of society?  All because a few sociopaths found a way to use technology to kill people more efficiently than in the past before the international community rose up and stopped basically every last one of them?  Dude, life's not perfect, but get some perspective!

[Skill and Chance]

Much of the 20th century was terrible, unfathomably horrible events, I wouldn't mind a do-over.

So you'd rather go back to 40 year average lifespans, 2-3% risk of death in childbirth per birth, uncontrolled infectious disease in general, much more violent crime, and slavery/a severe racial caste system being a fundamental feature of society?  All because a few sociopaths found a way to use technology to kill people more efficiently than in the past before the international community rose up and stopped basically every last one of them?  Dude, life's not perfect, but get some perspective!

What are you talking about? Genocide, ethnic cleansing, human-organized famine, and the like aren't aberrations or isolated incidents, they are the direct product and natural result of the process of "modernization" that was such a fixation in the 19th and 20th century and which continues to reap horrendous consequences around the world.

You don't get the 80 year lifespans with virtually all children living to adulthood, antibiotics, social security, political rights for women and the end of most overt racial discrimination without global capitalism, free trade and some level of democracy.  It's a package deal.  And yes, there's severe inequality, but 80%+ of the world is still better off than the subsistence farmers of the 18th century who made the equivalent of a few $100 to a couple $1000 in today's money per large family per year.  And there's some pollution etc. to deal with, but even if we messed with the environment so badly that we collectively lost half the arable land on the planet, most people would still be better off than in 1750.