More than $2 million has been spent on ads this year in the Senate Democratic primary in Montana. And almost every cent has come from a pair of dueling super PACs whose sources of funding remain a mystery.

The two Democratic candidates in the race haven’t spent anything on TV or digital ads in the state, according to AdImpact, giving the super PACs outsize influence on the outcome of Tuesday’s primary.

It’s a strikingly common dynamic in Democratic primaries this year, including in a plethora of races this month.

To a degree without modern precedent, the Democratic Party’s House and Senate primaries are being inundated with spending from outside groups, which has frustrated Democratic voters and had a major effect on the outcome of some races. In nearly every case, the funding source for the ads is unknown, and in many cases, an ad’s subject matter appears deliberately misaligned with a group’s actual goals.

The overall effect is such that these groups — backed by wealthy special interests, Democratic leaders or even Republican officials trying to affect their opponents’ races — have displaced campaigns themselves as the most influential entities in the campaign.

“Democratic candidates are facing an unprecedented amount of outside spending, both from Democratic-aligned groups trying to mold outcomes — based on ideological or electability — and Republican dark money groups meddling to elevate weak candidates,” said Ian Russell, a longtime Democratic strategist.

Outside groups have spent heavily in Democratic primaries previous election cycles, but the practice is now more widespread “by several times over,” Russell said.

The deluge first arrived in a quartet of Chicago-area House races in March, where outside groups spent more than $26 million on electioneering activities. It has continued in races this month, including in Iowa, where the outside group VoteVets has spent nearly $10 million in support of state Rep. Josh Turek in a competitive two-way primary there. In Michigan, a group called the Center for Democratic Priorities has spent about $6.5 million boosting Rep. Haley Stevens in her three-way race ahead of the state’s August primary.

A group of super PACs widely believed to be linked to Republicans have engaged in primary races happening this month, including in California, New Jersey and Maine, spending more than $5 million on ads that appear to be designed to boost Democratic candidates the Republican Party considers electorally weaker general-election nominees.

And in New York’s high-profile Democratic primary in the 12th Congressional District, outside groups account for four of the top five spenders so far, according to AdImpact. These groups, led by super PACs connected to the AI industry, have spent nearly $10 million between them.

Democrats say the spending surge is a result of a perfect storm of factors, including the rise of industries like AI and crypto that have deep pockets and an interest in shaping government regulation. More than anything else, however, they point to the massive number of competitive Democratic primaries this year, driven in part by a restless liberal base less willing to accept the candidates backed by party leadership.

The division has created a new opening for outside players to try to influence the outcome.

“It’s never felt like there have been this many primaries for this many big seats,” said Amanda Litman, co-founder of the liberal group Run for Something. “Which is indicative of how much the establishment or old guard has lost control. Because in previous cycles, they would have been able to box candidates out.”

Super PACs have been a factor in Democratic primaries since their inception following the Supreme Court’s 2010 Citizens United decision. In 2022, following redistricting, groups had spent more than $50 million attempting to influence primaries, according to Politico.

But Democratic voters are reacting to this year’s spending from outside groups with uncommon frustration. In Iowa, for example, VoteVets’ spending to boost Turek has helped make him the favorite in Tuesday’s primary against state Sen. Zach Wahls, in part because the nearly $10 million the group has spent is three times more than the combined amount spent by Turek’s and Wahls’ campaigns.

VoteVets’ mission is to support candidates who served in the armed forces, and Turek is not a military veteran. Leaders with the group have defended their decision because Turek suffers from spina bifida after his father, a military veteran, was exposed to Agent Orange in Vietnam.

That explanation doesn’t satisfy some Wahls supporters, who allege that the group is secretly acting on behalf of Senate Democratic Leader Chuck Schumer. Wahls has said he would not support Schumer as leader if elected.

“The question to ask VoteVets is, how many times have you financially supported, at this level, the child of a veteran? And the answer is none. There’s zero,” said Scott Foens, a Wahls supporter and former chair of the Iowa Democratic Party’s Veterans’ Caucus.

“So then it becomes a question of OK, why? What’s going on here behind the scenes?” he said.

Representatives for Schumer have repeatedly denied that he is behind the pro-Turek spending, and VoteVets officials have said they have previously supported nonveterans running for office, like Sen. Raphael Warnock of Georgia, when the group considers their candidacies essential to preserving government support for institutions like Veterans Affairs.

But because of Federal Election Commission reporting rules, VoteVets will not have to disclose all of its donors by the time Iowa Democratic voters cast their ballots Tuesday. And critics point out that the group has spent nearly as much on independent expenditures in the Iowa Senate race as it did on all races in 2024 and does not even list Turek as one of their endorsed candidates this year.

“As a veteran, I’m annoyed that vets are being used here,” said one Democratic strategist who served in the military and requested anonymity to speak candidly. “I think in the end it’s the VoteVets brand that’ll be tarnished in all of this, because it’s a stretch to back him in this scenario.”

Like VoteVets, the Center for Democratic Priorities has not yet disclosed its donors, though its spending in Michigan might already be boosting Stevens’ support.

The situation is similar in Montana. More Jobs, Less Government — a Republican group that previously supported Republican Sen. Tim Sheehy — has spent more than $1 million since May on ads targeting one of the Democratic candidates, former state Rep. Reilly Neill. The spots play up her opposition to President Donald Trump and appear designed to boost her in a Democratic primary.

Another group, Progressive Vote PAC, has spent more than $1 million backing a different candidate in the race, Alani Bankhead, according to AdImpact. That group, which formed in April, has thus far only reported a single $200,000 contribution, one from another outside group called American Values Project PAC.

Democrats in the state are grappling with the possibility of backing an independent candidate for Senate: Seth Bodnar, a former president of the University of Montana.

His ad spending is being dwarfed by outside groups’: Bodnar’s team has spent about $300,000 on ads, according to AdImpact.