THE PARTY OF CIVIL RIGHTS…. Given the new-found electoral relevance of the Civil Rights Act, I suppose this was inevitable.

The GOP went there. In an email sent to reporters in the height of the Rand Paul firestorm yesterday, the NRSC defended its Senate nominee in Kentucky by pointing out that it wasn’t Republicans who were the most vocal opponents of the 1964 Civil Rights Act when it was in Congress.

“As a side note, I would point out the irony – which seems to have been lost in some of the news coverage — that the same party seeking to manufacture this issue today, is in fact the same political party which led the filibuster against the Civil Rights Act in 1964,” NRSC spokesperson Brian Walsh wrote.

This comes up from time to time, whenever Republicans are feeling particularly defensive about the civil rights issues. But in light of the party’s confusion, it’s probably time for a quick refresher.

The Democratic Party, in the first half of the 20th century, was home to competing constituencies — southern whites with abhorrent views on race, and white progressives and African Americans in the north, who sought to advance the cause of civil rights. The party struggled, ultimately siding with an inclusive, liberal agenda.

As the party shifted, the Democratic mainstream embraced its new role. Republicans, meanwhile, also changed. In the wake of Democratic President Lyndon Johnson signing the Civil Rights Act, the Republican Party welcomed the white supremacists who no longer felt comfortable in the Democratic Party. Indeed, in 1964, Republican presidential nominee Barry Goldwater boasted of his opposition to the Civil Rights Act, and made it part of his platform. It was right around this time when figures like Jesse Helms and Strom Thurmond made the transition — leaving the Democratic Party for the GOP.

In the ensuing years, Democrats embraced their role as the party of diversity, inclusion, and civil rights. Republicans became the party of the “Southern Strategy,” opposition to affirmative action, campaigns based on race-baiting, vote-caging, discriminatory voter-ID laws, and politicians like Helms and Thurmond.

Indeed, as the chairman of the Republican National Committee recently conceded, his party deliberately used racial division for electoral gain for the last four decades.

Just a minor detail, which seems to have been lost in some of the news coverage, and which the NRSC might have forgotten.

Update: For the record, 46 Democrats and 27 Republicans voted for the Civil Rights Act, while 21 Democrats and 6 Republicans opposed.

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Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.