At what point did the Southern Strategy begin?

[Adam_Trask]

The basis for the Solid Democratic South was simple; it was the promise that the Democratic Party would support Democratic Presidential candidates in exchange for non-interference in the internal affairs of the Southern States.  It was the assurance that segregation would not be interfered with by the Federal Government.  The only exceptions in this period was 1920, when Warren Harding (to everyone's shock) carried Tennessee, and 1928, when VA, NC, TN, FL, and TX carried for Republican Quaker Herbert Hoover over Democratic Catholic Al Smith.  Hoover and Harding has no "Southern Strategy", however; the anti-Catholic sentiment and support for Prohibition simply allowed Hoover to carry the Border South (save Arkansas, whose Senior Senator, Joseph Robinson, was Smith's running mate).  (This manifested in situations such as Sen. Theodore Bilbo (D-MS), was probably the most vile racist in the history of the 20th century US Senate, having a record of down-the-line support for the New Deal.)  The only sign of unrest in all of this was when conservative Democrats in Texas nominated a slate of Democratic electors called the "Texas Regulars"; they were an independent slate of electors opposing FDR in 1944.  They received about 100,000 votes, nowhere enough to win.

Broadly, this seems right to me. However, I think the unrest in the southern Democratic Party with the New Deal is somewhat more prominent/important than you're suggesting here.

Although FDR was more than capable of whipping the votes of Southern Democrats, I think segments of the southern Democratic Party were much more uncomfortable with the New Deal than is oft suggested (albeit, acknowledging there were plenty of economically progressive southern Democrats, too, both before and during the New Deal era). While it didn't behove those skeptical southern Democrats to buck the New Deal because they were paid handsomely for their support through programs that directed a lot of New Deal money towards the South, there were some seeds of their discontent that can be seen as early as 1935.

In 1935, southern Democrats were given a fairly important exception to the expansion of the Fed's power over labor relations (which I think is probably the area in which they were the most uncomfortable with the New Deal). The Social Security Act of 1935 specifically excluded domestic workers and agricultural workers. Black southerners did this work, and the exclusion of domestic workers and farm workers simply does not make sense without this context (fyi: the SSA wrote a hilarious article trying to deny that this exclusion was racially motivated by drawing on some scant legislative history, but their argument is pretty weak and doesn't capture the Administrations frequent backroom dealing with Southern Dems, imo – check it out if you're interested).

I think this carve-out strongly suggests that Southern Democrats were more broadly skeptical of the New Deal – even if they supported it throughout FDR's presidency. But even if you're not willing to go that far, there's an underlying logic to this important carve-out which points to  the kind of discomfort (the seeds of discontent) a Southern Democrat would have with the New Deal's transformative effects on the American economy. And I think too shows why the South became more comfortable with the Republican Party throughout the 20th century. Yes, civil rights was the issue that led to the party swap in the South, but the post-New Deal Democratic Party's economic policies did not suit the southern ruling classes's interests.

Ultimately, I think what I'm arguing is that it's more than just integration of the Army and Truman's support of some Civil Rights measures that led to the Dixiecrat revolt. I think the discontent had been brewing for some time and was related to economic issues that would become increasingly important to white southerners (particularly wealthy white southerners) in the latter part of the 20th century accounting, in part, for the success of the Southern Strategy as opposed to some Southern third-party.

[Adam_Trask]

In 1935, southern Democrats were given a fairly important exception to the expansion of the Fed's power over labor relations (which I think is probably the area in which they were the most uncomfortable with the New Deal). The Social Security Act of 1935 specifically excluded domestic workers and agricultural workers. Black southerners did this work, and the exclusion of domestic workers and farm workers simply does not make sense without this context (fyi: the SSA wrote a hilarious article trying to deny that this exclusion was racially motivated by drawing on some scant legislative history, but their argument is pretty weak and doesn't capture the Administrations frequent backroom dealing with Southern Dems, imo – check it out if you're interested).

This is the Ira Katznelson thesis from "When Affirmative Action Was White", which I remember doesn't hold up to scrutiny in this instance. Interesting review of the evidence for why domestic and agricultural workers were excluded from Social Security in this. It notes that about three times as many white workers were excluded as black, that there was no unified Southern opposition to the inclusion of agricultural and domestic workers, that every unemployment insurance scheme in Europe before 1935 excluded either or both categories of workers, and the architects of Social Security in the administration, inspired by those European programmes, were concerned with the administrative difficulties in covering informal workers like farm labourers and servants. For example it notes that Senator Tom Connally of Texas, who wiki says "led the opposition to federal anti-lynching legislation in the late 1930s, filibustering the Anti-Lynching Bill of 1937", actually advocated for the inclusion of agricultural workers out of a concern that they would be excluded from the benefits.

Probably the most relevant passage to the general discussion about Southern Democrats and the New Deal:

Southern Democrats acted in concert against Northern Democrats only nine times between 1933 and 1949: five times to block anti-lynching legislation, twice against wage increases for the Works Progress Administration, once against an antidiscrimination provision in federal education financing, and once against a Fair Employment Practices measure. Southern Democrats failed to display their characteristic "solid" tendencies for the other 580 roll call votes (...) As a whole, southern legislators were more liberal than northerners between 1933 and 1937.* The one additional issue that tended to unite southern Democrats was the strong concern that federal funding should not be biased against their region.

Circling back to this point, Katznelson defended his thesis in a recent Boston Review article.  

Taking into account the evidence you marshal here, Katznelson argues:

"Nonetheless, the legislative history of the Social Security Act supports the race-centered argument. The basis for congressional action, [a] report by President Franklin Roosevelt’s Committee on Economic Security, unambiguously stated, “We are opposed to exclusions of any specific industries within the Federal act.” Focusing on persons at the bottom of the wage scale, the document explicitly stressed that “agricultural workers, domestic servants, [and] home workers” must be included. Following this explicit advice, the bill the White House sent to Congress included these groups. Only when the legislation was considered in the House Ways and Means Committee, which was chaired by Robert “Muley” Doughton of North Carolina, and in the Senate Finance Committee, which was chaired by Pat Harrison of Mississippi, were the occupational categories removed from the legislation."