On the day of the Indiana Democratic primary, Bernie Sanders told supporters in Louisville that American voters won't elect Republican front-runner Donald Trump president. Here are key moments from his May 3 rally. (Reuters)

The relationship between the Democratic National Committee and Sen. Bernie Sanders (Vt.) grew more heated Saturday after the DNC rejected his campaign’s request for the removal of the co-chairs of the standing committee on rules.

In a letter sent Friday, the Sanders campaign labeled the committee co-chairs, former congressman Barney Frank (Mass.) and Connecticut Gov. Dan Malloy, as “aggressive attack surrogates” for the Clinton campaign, whose criticism had “gone beyond dispassionate ideological disagreement and have exposed a deeper professional, political and personal hostility toward the senator and his campaign.”

The Sanders campaign built a case out of interviews both co-chairs had given as the party grew worried about Sanders’s refusal to drop out until “the last ballot” was cast.

“In a March interview, Mr. Frank defamed Senator Sanders as ‘outrageously McCarthyite,’” Sanders campaign counsel Brad Deutsch wrote in the letter to the DNC. “Malloy has even ventured that Senator Sanders should be ‘held accountable’ for the ‘death and destruction’ cause by his ‘mistake.’”

The DNC responded in less than 24 hours, mentioning none of the ad hominem criticisms that Malloy or Frank had made. Instead, Jim Roosevelt and Lorraine Miller, co-chairs of the Rules and Bylaws committee, said that the Call for the 2016 Democratic National Convention had duly elected Frank and Malloy in January.

“Your challenge does not allege that there was any violation of the provisions of the Call in the conduct of their elections,” they wrote. “Having carefully reviewed your challenge, we find that it fails to meet the criteria.”

The Sanders campaign’s frustration with Frank and Malloy was a reflection of the strange (and perhaps temporary) enemies made during the long primary. Frank, one of the most quotable figures in politics, was elevated as a critic of Sanders’s personality and tactics.

“The way he’s been acting now is a demonstration of why he’s had no support from his colleagues,” Frank told The Washington Post this month. “The problem that most committed liberals have had with Sen. Sanders is that we don’t think his approach is effective. It’s a self-righteous view that if you just say something loudly enough, you win.”

Frank, the longest-serving openly gay congressman, effectively capped off his career with the passage of major financial reforms — including the creation of the Consumer Finance Protection Bureau.

Malloy, who beat the 2010 Republican tide to win a close election, was long seen as a progressive experimenter. While Republican-run states cut back on benefits and public employees, Malloy raised taxes, presenting Connecticut as a laboratory of democracy to contrast with Kansas or Texas. This year, however, Malloy’s approval ratings cratered as he proposed a compromise, cost-cutting budget to close the state’s deficit.

In an interview on Saturday night, Frank was unapologetic about his criticism of Sanders, saying again that it was "McCarthyism" to link any part of the government's response to the 2008 finanicial crisis with Clinton's paid speeches to Goldman Sachs.

"If some issue would come up where an interpretation from the Rules Committee would change the outcome, I’d recuse myself," said Frank. "The fact is, that's not happening, and she's winning the nomination even if you don't count the superdelegates. What worries me is that when Bernie raises doubts about this sort of thing, it stokes the false impression that the nomination is being stolen."

Frank also said it was false to assume he had a "25 year vendetta" against Sanders.

"About 10 years ago, or 12 years ago, at his request as a senior member of the House Financial Services Committee, I went to Burlington to speak at a fundraiser for him," said Frank. "I hope, for the sake of his purity, that no bankers snuck into the room. And I hope he will release the list of the attendees from that fundraiser, just to make sure."

The full letter from the Sanders campaign is below:

This firm serves as legal counsel to Bernie 2016, Inc. (the "Campaign"), the official campaign committee for Senator Bernie Sanders' 2016 U.S. presidential bid. We submit this letter on behalf of the Campaign, pursuant to Rules II(A), II(C), VII(B)(5), VII(F)(3), VII(G) and VII(H) of the DNC's Call for the 2016 Democratic National Convention (the "Call"), and Regulations 3.1(C) and (D) of the Regulations of the Rules and Bylaws Committee (the "RBC Regulations"), to commence formal credentials challenges and contests against Governor Dannel Malloy, appointed Co-Chair of the Standing Platform Committee, and former Representative Barney Frank, appointed Co-Chair of the Standing Rules Committee for the 2016 National Convention (the "Convention"), or alternatively to seek advisory opinions concerning the fitness of these individuals to serve in their appointed roles.

Both Governor Malloy and Mr. Frank (the "Chairs") have been harsh, vocal critics of Senator Sanders, and equally active supporters of his challenger, Hillary Clinton. While it is expected, acceptable, and even desirable, that committee members and leaders at the Convention will represent a diversity of political views and presidential preferences, the preferences of party officials must not interfere with the fair and neutral administration of Convention business and procedures. Governor Malloy and Mr. Frank have both been aggressive attack surrogates for the Clinton campaign. Their criticisms of Senator Sanders have gone beyond dispassionate ideological disagreement and have exposed a deeper professional, political and personal hostility toward the Senator and his Campaign. The Chairs therefore cannot be relied upon to perform their Convention duties fairly and capably while laboring under such deeply held bias. The appointment of two individuals so outspokenly critical of Senator Sanders, and so closely affiliated with Secretary Clinton's campaign, raises concerns that two of the three Convention Standing Committees are being constituted in an overtly partisan way designed to exclude meaningful input from supporters of Senator Sanders' candidacy. The Campaign respectfully but emphatically requests, under the qualification standards clause of the Call, that both Governor Malloy and Mr. Frank be disqualified from their respective positions with the Standing Platform and Rules Committees.

I. Barney Frank

Mr. Frank's animosity toward Senator Sanders dates back decades. In 1991, while serving alongside Senator Sanders on the House Financial Service Committee, Mr. Frank accused Senator Sanders of "unduly denigrating] the institution and a lot of the members” of Congress. After Senator Sanders won the New Hampshire Democratic presidential primaries in February, Mr. Frank wrote an opinion piece in which he professed his "resentment" toward the Senator.

And Mr. Frank's invective against Senator Sanders has only intensified as Senator Sanders has notched additional primary victories. In a March interview, Mr. Frank defamed Senator Sanders as "outrageously McCarthyite." When asked to confirm that he considered Senator Sanders' supporters to "have a slightly unrealistic sense about the political process," Mr. Frank answered glibly; "I didn't say slightly." When the same interviewer paraphrased that "the argument that people like Sanders would make is that, the financial system is corrupt fundamentally," Mr. Frank responded bluntly: "if that's the case it's even dumber than I thought." The Campaign has justifiable significant doubts, in light of his past and present comments, about whether Mr. Frank is capable of respecting Sanders supporters, and what he has called their "dumb" and "unrealistic" viewpoints.

An individual so harshly dismissive of views held by 45 percent of the Party's constituency is not qualified to serve as an even-handed or effective leader at the Convention. The CoChairs of the Standing Rules Committee hold broad power to submit resolutions and measures for vote on the floor of the Convention. It is imperative that this power be wielded by someone who respects, and is inclusive of, opposing viewpoints. Mr. Frank's barbed remarks toward Senator Sanders and his supporters demonstrate that Mr. Frank is not such a person, The Campaign thus respectfully demands that Mr. Frank be disqualified as Co-Chair of the Standing Rules Committee.

II. Dannel Malloy

Governor Malloy has candidly admitted that he "will continue to work hard to make sure [Hillary Clinton] is elected president of the United States this November," a pledge that the Campaign justifiably believes would influence his work as Co-Chair of the Standing Platform Committee. Not only is Governor Malloy an avowed loyalist of the Clinton Campaign, he is an incendiary critic of Senator Sanders.

While justly criticizing "Donald Trump and his extremist agenda" in press remarks, Governor Malloy has gone on to draw pejorative comparisons between Mr. Trump and Senator Sanders. Governor Malloy has unfairly ascribed blame for national gun control laws single-handedly to Senator Sanders, referring to the three-day wait provision of the Brady Bill as the "Charleston-Sanders loophole." Malloy has even ventured that Senator Sanders should be "held accountable" for the "death and destruction" cause by his "mistakes."

Such exaggerated and divisive criticisms betray a closed mind and a lack of civility that would make it difficult if not impossible for Governor Malloy to effectively conduct his duties as Co-Chair of the Standing Platform Committee. In this role, Governor Malloy will be tasked with direction and oversight of a platform embodying the party's core principles. This platform should be as inclusive as possible, expressing where practicable the input of the significant percentage of Democrats who support Senator Sanders. The Campaign has legitimate concerns that Governor Malloy's open animosity toward Senator Sanders will make him unreceptive or even antagonistic to the viewpoints of these voters. The foreseeable exclusion of such a large constituency from this process would be damaging not only to the Campaign and its supporters, but to the DNC's own efforts to unify the party.

III. Conclusion

The Campaign does not object to the credentials of the remaining Co-Chairs or Vice-Chairs of either Standing Committee, and sees no reason that one Chair, supported by four Vice-Chairs, could not capably lead each of these groups. The Campaign has no doubt that the Standing Platform and Rules Committees will run more transparently, Fairly and smoothly if their leadership is free from influence by self-proclaimed partisans intent on marginalizing Campaign supporters.

Accordingly, the Campaign respectfully requests that this Committee disqualify Governor Malloy and Mr. Frank or, in the alternative, provide a hearing followed by an advisory opinion concerning the fitness of the Chairs to serve in their appointed roles under Regs. 3.1(C) and (D) of the RBC Regulations.

If this Committee is unable to provide its advice or assistance pursuant to the RBC Regulations, the Campaign will seek resolution of these issues by presenting its objections in motions as the first items of business at the initial meetings of the Standing Platform and Rules Committees and, to the extent necessary, will request the drafting and adoption of minority reports from both Standing Committees for presentation to the floor of the full Convention.