“We commend you on running a spirited campaign that has energized and mobilized a new generation of voters, but we are concerned about the way you and your campaign have characterized the South,” write South Carolina Democratic Party Chairman Jaime Harrison, Louisiana Democratic Party Chairwoman Karen Carter Peterson, Florida Democratic Party Chairwoman Allison Tant, Democratic Party of Georgia Chairman DuBose Porter, Mississippi Democratic Party Chairman Rickey Cole, former South Carolina Gov. Jim Hodges, and former Democratic National Committee Chairman Don Fowler, each of whom now supports Clinton.

“The greatest asset we have as a party is our diversity — a diversity of cultures, religions, ethnicities, and backgrounds. Yet over the course of this Democratic primary, you and your surrogates have sought to minimize Secretary Hillary Clinton’s victories throughout the South as a symptom of a region that, as you put it, ‘distorts reality.’ You argue that the South is ‘the most conservative part’ of America; implying states that traditionally vote Republican in a general election are not worth contesting in a Democratic primary.”

Even for sitting party officials who support Clinton, the act of sending such a missive is an unusual move — in the interest of party unity, many prefer not to show any preference between competing candidates when acting in their official capacity. But the Vermont senator’s statements have become a source of constant chatter for high-level Democrats across the South.

“I think that having so many Southern states go first kind of distorts reality,” Sanders said during a taping of “The Nightly Show” on Comedy Central earlier this month, presumably referring to Clinton’s dominant primary wins in South Carolina, Alabama, Arkansas, Georgia, Tennessee, Texas, Virginia, Louisiana, Mississippi, Florida and North Carolina — some of which the Sanders campaign wrote off as Clinton territory from the start.

That comment echoed on the Brooklyn debate stage a few days later, when Sanders said “Secretary Clinton cleaned our clock in the Deep South. No question about it, we got murdered there. That is the most conservative part of this great country.” Many Southern Democrats were also upset when a Sanders surrogate and introducer, actor Tim Robbins, said at one event that Clinton’s victory in South Carolina — the fourth state to vote, and the first with a large African-American population — was “about as significant” as winning Guam.

In the letter, sent one day after Sanders’ bracing defeat in New York, the party leaders note that the senator’s wins in Oklahoma, Utah and Idaho came in more conservative parts of the country than the South, and that some Southern Democrats in Congress who represent majority-minority districts are among the most liberal in the House of Representatives.

Pointing to the role African-American voters played in Clinton’s wide wins in the South, the signatories to the letter — some of whom have been long-time Clinton supporters, but others of whom stayed neutral until after Clinton won their primaries — note that black voters have “been the most reliable and consistent vote for the Democratic Party for a generation,” pointing to statistics showing black voters represented between 31 and 71 percent of the Democratic electorate in South Carolina, Georgia, Mississippi, Louisiana, Alabama and North Carolina in 2016.

While the letter finishes by praising Clinton, it does not explicitly note that some strategists and Democrats aligned with her campaign are looking closely at opportunities for the party gains in Southern states like North Carolina and Georgia at the presidential level this year — especially if Trump is the Republican nominee and Democrats can drive up turnout among minority voters. Dismissing that possibility, many worry, could threaten the South’s ability to attract financial and political support from within the party.

South Carolina, like Nevada in the West, was added to the front of the primary process partially because of its diversity, the letter notes, reminding Sanders of fellow Vermonter and former Democratic National Committee chairman Howard Dean’s famous “50-state strategy.” In addition, the letter reminds, in an election year when many Democrats are starting to think seriously about competitive opportunities in House and local races, then-Sen. Barack Obama’s 2008 organization in Southern primaries helped lay the groundwork for party wins in North Carolina, Virginia and Florida.

“Democrats ought to embrace the South and all regions to build an organization that can compete in all 50 states,” the letter reads. “We must continue winning states like Virginia and North Carolina, and we can’t write off states like Tennessee and Georgia. Even Texas could turn blue in less than a generation. And beyond the presidential race, there are important statewide and other federal races happening every cycle. Boosting Democrats’ chances in those states is vital to enacting a progressive agenda at the local level and in General Assemblies. This can only happen if we show up, speak to the region’s needs, and compete for every vote, even in the face of long odds. That’s how change really happens.”