Why have Republicans hated Obama from the 1st day of his term, more than any previous Democratic President?

They hated Clinton and Carter, but not even close to the rage they direct toward President Obama, from the Tea Parties, to the allegations of racism, to the shouting down of any and all contrasting views at Town Halls, to the birther movement... and on and on. Why Obama more than any previous Democratic President, not just around health-care reforms, but from day one of his Presidency?