A pair of largely overlooked U.S. House races in D.C.'s Maryland suburbs are racing up the leaderboard of the most expensive congressional primaries in U.S. history.

Why it matters: The volume of cash pervading the Democratic primary for Maryland's 5th and 6th congressional districts has some candidates raising the possibility that there is such a thing as too much spending for a favored candidate.

• Voters "see the frequency of the ads, and now they're asking questions," said Wala Blegay, a Prince George's County Council member running in Maryland's 5th District.
• Said former Capitol Police officer Harry Dunn, another candidate in the 5th District who's a darling of the liberal grassroots and endorsed by former Speaker Nancy Pelosi (D-Calif.): "It's tough to square, like, why is someone donating this much money?"

Driving the news: Outside groups — most notably the pro-crypto super PAC Protect Progress and AIPAC's United Democracy Project — had spent a combined $12.5 million in Maryland's 5th District as of today, according to FEC filings.

• The candidates in the Democratic primary to succeed former House Majority Leader Steny Hoyer have spent a combined $10.5 million as of June 3.
• On the other side of D.C.'s suburbs in the 6th Congressional District, Rep. April McClain Delaney (D-Md.) has loaned her campaign $7.4 million as she tries to withstand the staggering $25 million that her predecessor, David Trone, has loaned his campaign.

By the numbers: Super PAC spending in the 5th District has almost all favored state Del. Adrian Boafo, who is backed by Hoyer, Maryland Gov. Wes Moore and Sen. Angela Alsobrooks.

• Hoyer's AmeriPAC, Congressional Black Caucus-aligned Rolling Sea Action Fund and the American Bridge-affiliated Project 218 have also spent six-figure sums supporting Boafo.
• Just one group — Servant-Leader Fund, which supports Democratic veterans running for office — has spent for another candidate, putting down $135,000 to support former state Del. Rushern Baker.

What they're saying: Dunn said of the outside spending in an interview with us, "I've been one of the top fundraisers in the country, and I can't compete with that. It's tough to overcome."

• "The entire experience has been so frustrating because almost none of the ads that people have seen on TV have said, 'Adrian Boafo for Congress,'" said Blegay.
• "People are seeing them about every hour," she added. "It doesn't take $12 million to win this race, and that's just how much money they've put in."
• Boafo's campaign did not respond to repeated requests for an interview.

The intrigue: McClain Delaney and Trone are both considered moderate, establishment-aligned Democrats.

• Other Democrats in the 6th District primary have raised paltry sums by comparison, such as progressive former Consumer Financial Protection Bureau official Alexis Goldstein.
• McClain Delaney and Trone have been running ads playing up their progressive bona fides and whacking each other as insufficiently anti-Trump, anti-ICE or pro-abortion rights.

— Andrew Solender

"No more Chuck Schumer," declares Rep. Seth Moulton in a new ad for the Massachusetts Democratic Senate primary.

Why it matters: Moulton, 47, is invested in the Democratic Party's generational warfare.

• His campaign is putting at least $1 million into the "Gung Ho" ad campaign that includes his broadside at the Senate minority leader, the Boston Globe reports.
• Moulton is challenging Sen. Ed Markey, 79, who has served in Congress since 1976.

— Justin Green

New York's congressional primary tomorrow will be a key test of strength for the left-wing movement challenging the Democratic Party's establishment.

Why it matters: Several races pit the interests of House Minority Leader Hakeem Jeffries against those of democratic socialist NYC Mayor Zohran Mamdani.

• Mamdani, one of the left's most prominent figures in New York and nationwide, is backing three left-wing insurgents vying for NYC-based House seats.
• Two of those insurgents are running against incumbent Democrats — and Jeffries almost always supports his incumbents.

State of play: In the state's 10th District, Jeffries is supporting Rep. Dan Goldman (D-N.Y.) while Mamdani is backing NYC Comptroller Brad Lander.

• In the 13th District, Jeffries-backed Rep. Adriano Espaillat (D-N.Y.) faces a spirited challenge from Mamdani-endorsed democratic socialist Darializa Avila-Chevalier.
• In the 7th District, Mamdani is supporting democratic socialist State Assembly member Claire Valdez over Brooklyn Borough President Antonio Reynoso, though Jeffries hasn't endorsed in that race.

Yes, but: Mamdani has avoided more direct confrontations with Jeffries, most notably opposing City Council member Chi Ossé's aborted attempt to primary the Democratic House leader.

• These also aren't perfectly clear-cut battles of left vs. center: Goldman and Espaillat are both members of the Congressional Progressive Caucus but have come under fire from the left in part for their support of Israel.
• Things get even more complicated in the 7th, where Reynoso is backed by retiring progressive Rep. Nydia Velázquez and the Working Families Party, which also supports Lander.

— Andrew Solender