It should be rather obvious that the republican part is the party of white people. More specifically white people who are very religious, fairly rich and hold racist views of non-whites. The common belief of those on the left is that this began with Nixon after the the civil rights acts were passed. But it goes back further than that. To end of Franklin Roosevelt's fourth term. FDR had made a deal with the Dixiecrats. if they would support his New Deal legislation - the CCC WPA Social Security - the democratic party and the government would turn a blind eye with what they did and how they did it. The democratic party at the 1948 convention had just approved a civil rights platform, one that was mild and vague and ambiguous enough not to offend the South. The liberal wing however were incensed by this and the them mayor of Minneapolis - Hubert Humphrey - vowed to take the fight to the delegates.

The liberals' plank included anti-lynching and anti-poll tax legislation, ending segregation in the armed forces, supporting fair employment laws. All were positions the nominee-to-be, Harry Truman, supported. - SFGate

The convention roared it's approval and the southern Dixiecrats walked out. They held their own convention and nominated Strom Thurmond as their candidate.

Truman won the election of 1948 without the Dixiecrats though. But FDR himself wanted to rid the party of the "reactionary elements" in the south and in 1944 said to one of his advisers, ". . . the time has come for the Democratic Party to get rid of its reactionary elements in the South and attract to it liberals in the Republican Party." Lead by Wendell Wilkie. But Wilkie died before the 1944 election and the liberals that followed him fell apart.

So instead of attracting these liberals into the democratic party, it left the door open for the southern Dixiecrats. The southern states had their own reasons for hating the democratic party's stance on unions and labor and social contracts. These things meant that they would have to treat blacks the same as whites and this they would never do. Unions had black members and so unions were anti-south. Equal education and voting was also considered anti south.

But what the politicians of the time neglected to consider was that outside the metro areas in the northern and central states, a lot of whites held similar beliefs as those in the south. So when the civil rights acts were passed by congress and signed by LBJ, white resentment swelled from Alabama to Idaho and Oregon to Main in the predominantly white small towns and rural areas. Reagan's meme of the "Welfare Queen" hit a nerve with those folks as well and the republicans knew it.

But overall demographics are changing and a party of all white christian males is on the decline and they know this as well.

A Republican strategist said something interesting and revealing on Friday, though it largely escaped attention in the howling gusts of punditry over Mitt Romney’s birth certificate crack and a potential convention-altering hurricane. The subject was a Ron Brownstein story outlining the demographic hit rates each party requires to win in November. To squeak out a majority, Mitt Romney probably needs to win at least 61 percent of the white vote — a figure exceeding what George H.W. Bush commanded over Michael Dukakis in 1988. The Republican strategist told Brownstein, “This is the last time anyone will try to do this” — “this” being a near total reliance on white votes to win a presidential election. . . . . .

Blowing up the welfare state and affecting the largest upward redistribution of wealth in American history is a politically tricky project (hence Romney's belief that he may need to forego a second term). Hence the Romney campaign's clear plan to suture off its slowly declining but still potent base. Romney’s political-policy theme is an unmistakable appeal to identity politics. On Medicare, Romney is putting himself forward as the candidate who will outspend Obama, at least when it comes to benefits for people 55 years old and up. Romney will restore the $700 billion in Medicare budget cuts imposed by Obama to its rightful owners — people who are currently old.

He will cut subsidies to the non-elderly people who would get insurance through Obamacare — a program that, Romney’s ads remind older voters, is “NOT FOR YOU.” Romney’s repeated ads on welfare, blaring the brazen lie that Obama has repealed the welfare work requirement, hammer home the same theme. The purpose is to portray Obama as diverting resources from us to them.

In their heart of hearts, Romney and Ryan would probably prefer a more sweeping, across-the-board assault on the welfare state. But the immense popularity of the largest, middle-class social insurance programs like Medicare and Social Security force them into the divide-and-conquer gambit. They can promise to hold their disproportionately old, white base harmless and impose the entire brunt of their ambitious downsizing of government on young, poor, and disproportionately nonwhite Democratic constituencies. - New York Magazine