A Democratic House primary in Massachusetts has turned into a fight over hidden outside money, and it's bad news for candidates running without big donors.

• Two super PACs are spending heavily to boost state Rep. Tram Nguyen in the open 6th district race, and the money trail leads back to AIPAC.
• One PAC, Pro-Choice Majority Action, is funded mainly by a women's group fund that has taken more than $2 million from AIPAC's super PAC this cycle.
• Rival candidate Jamie Belsito says she was told directly to take the AIPAC, AI, and crypto money if she wanted the group's backing, and refused.
• A second super PAC backing Nguyen got its biggest check from her own state-level committee, two days before she launched her federal run — a move that skirts the ban on using state money in federal races.
• Innocuous-sounding PAC names let ads and mailers land without voters knowing who paid for them.

Outlook: The primary is Tuesday, and the spending is expected to grow in the final days.