I don't know when things started to go bad, but I can chronicle some of the milestones. Here are the highlights, I know I've missed some, but the pace is quickening in the 20th and 21st centuries.
1) 1620's: The first black slaves arrive in America. This presages centuries of civil strife.
2) 1860's: War between the States.
3) 1913: A pivotal year. 16th amendment allowing federal income tax and the 17th amendment, direct election of US senators. This is where things really started to go downhill.
4) 1930's: Federal government reaction to the depression.
5) 1960's: LBJ's "war on poverty" federalizes welfare.
6) 1990's: Clinton administration.
7) 2008-Present: Obama, America's moslem/communist/non-citizen/homosexual president actively pursues a pro-moslem, pro-communist, anti-American, pro-homosexual agenda. Majority of citizens reliant on federal government for their sustenance and soon, their health care.
I think the tipping point has been reached.