In their second hearing on anonymous campaign spending since the Supreme Court’s McCutcheon decision, members of the Senate Rules Committee sparred over the implications of the DISCLOSE Act, a bill which would require political nonprofits that spend more than $10,000 in a federal election to electronically disclose their major donors. The few senators who spoke at the hearing — Sens. Angus King, I-Maine, and Amy Klobuchar, D-Minn. were the only two left by the end — have all experienced the effect of dark money on elections, either directly or indirectly. But they have starkly different takes on what, if anything, Congress should do to reform the campaign system.

Minority Leader Mitch McConnell, R-Ky., was for disclosure before he was against it. Though he fought the 2002 McCain-Feingold bill on grounds that it did not do enough for disclosure, he has been one of the DISCLOSE Act’s most outspoken opponents. In a brief statement from the dais, McConnell called DISCLOSE a “crude intimidation tactic [from Democrats] masquerading as good government,” citing recent scandals at federal agencies as evidence of a larger effort by the Obama administration to stem free speech.

McConnell knows the effects of shadow money as well as any senator. Currently engaged in a bitter election battle with Democrat Allison Lundergan Grimes, he’s been aided by nondisclosing groups like the “Kentucky Opportunity Coalition,” which has spent more than $3.3 million on online, radio and TV ads attacking Grimes. Organized as a “social welfare” nonprofit, the group is not required to name its benefactors. The same goes for other shadowy groups playing in the Kentucky Senate race, like the benignly named Patriot Majority USA — a liberal nonprofit that has devoted a quarter of a million dollars to trashing McConnell and millions more targeting conservative candidates across the country.

Heather Gerken, a Yale professor who specializes in election law, told the committee in testimony that increased transparency receives broad bipartisan support among the electorate. But Brad Smith, president of the Center for Competitive Politics, countered that the current campaign finance system had more regulations than ever before and that the DISCLOSE Act would have a chilling effect on political speech — subjecting large donors to public harassment and threats if they supported unpopular causes.

Both McConnell and Sen. Ted Cruz, R-Texas, drew analogies to the civil rights era, when donor rolls to the NAACP in the deep south were kept anonymous to protect their supporters. They also noted that the Socialist Workers Party of America continues to enjoy an exemption from reporting its donors by the Federal Election Commission for their safety.

It’s a familiar line of reasoning for supporters of more anonymity in political giving. Conservative elections lawyer and campaign treasurer Dan Backer, who serves as legal counsel to Shaun McCutcheon, asked the commission in Nov. 2013 to grant an advisory opinion as to whether a similar exemption could be extended to the Tea Party Leadership Fund on the grounds that Tea Party supporters encountered “unprecedented harassment from both government officials and private actors.” Commissioners ultimately failed to grant the request in a 3-2 party line vote.

Cruz, veering into a discussion of another campaign finance bill — New Mexico Sen. Tom Udall’s proposed Constitutional amendment to overturn Citizens United — argued that Democratic sponsors were trampling the First Amendment in attempting to regulate the political speech of corporations.

Both sides of the debate agreed on one thing: dark money is not going anywhere soon.

“This is an important issue, it’s one that isn’t going to go away,” King said as he closed the hearing. “And I believe it’s going to continue to bedevil us for sometime unless we can some find resolution.”

As of publication non-disclosing groups have spent at least $33 million on federal races in the 2014 cycle, data from Real-Time Influence Explorer shows.