The New York Times' Manchin Vows to Block Democratic Voting Rights Bill and Preserve Filibuster includes the following passage:

Senator Roy Blunt, Republican of Missouri, praised Mr. Manchin, saying on NBC’s “Meet the Press” that “we need to move forward on election reforms in a bipartisan way. I look forward to being a part of that.”

But he was noncommittal on what he would support.

“We’ll see what happens with the John Lewis Voting Rights Act and other issues I think we can deal with, and deal with in a way that’s less partisan,” he said.

The House and Senate versions of the For the People Act were always something of a legislative Hail Mary. Democrats stitched together long-cherished goals such as advancing statehood for the District of Columbia; changes to redistricting laws in anticipation of a redrawing of House districts after the 2020 census; mandating early voting for 15 days before an election, 10 hours a day; and ending voter identification requirements.

Republicans labeled it a Democratic power grab, and even some members of the Congressional Black Caucus worried that its prohibition on partisan gerrymandering would end up costing Black representation in the South.

Question: How could the US Congress' H.R.1 – For the People Act of 2021 actually cost Black representation in the South by prohibition of partisan gerrymandering? Is it only because Black representation is currently and deliberately disproportionately enhanced or at least protected by some kind of partisan gerrymandering, or is it something more subtle?

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